Uses the github.com/ghodss/yaml library to convert YAML to JSON before
unmarshaling for the purposes of supporting YAML and JSON input while
converting to only support JSON internally.

Bug: T207694
Change-Id: I00668014907e9ea54917f5d5067cac08d0668053

The original design decision to install `node_modules` to a central
location outside the application directory was for a purported
development use case not yet realized. It has led to confusion and
unintended failures, and is just generally weird.

Let's right this wrong before it fossilizes into debt, like a hysterical
raisin in the sun.

Bug: T204591
Change-Id: I2e4797833471596b10b6b4a2705055050ca98ac6

The builder configuration has proven useful for supporting generic
pre-entrypoint commands such as dependency managers not otherwise
supported by specific Blubber configuration. Adding additional
`builder.requirements` config expands support for such commands by
allowing the user to specify files that should be copied into the image
before the builder command runs.

To support this extra configuration, `builder` had to be changed from a
simple string to a mapping. The builder command must now by given as
`builder.command`.

The pattern of creating parent directories, copying files, and executing
one or more commands prior to the entrypoint has become a common
one. Some of the implementation of this pattern was moved from
`PythonConfig` into shared build macros `build.SortFilesByDir` and
`build.SyncFiles`. All config types that must have requirements files
copied over independently of the entire source tree (`PythonConfig`,
`BuilderConfig`, `NodeConfig`) now delegate to these functions.

Change-Id: I67f33034f22cee2851ec866cfb07ab20c23eba8c

The `lint` rule was previous surfacing purely whitespace output of
`gofmt` as a failure and running `go tool vet` instead of `go vet` (the
former accepts source files as arguments, the latter takes package
names).

A real lint error in `config/node.go` was also fixed.

Change-Id: I7f13dcbb45a448f1ecac87e97527a7f4ed4d2c48

All import paths and other references to the previously Blubber repo in
Phabricator have been changed to point to the new Gerrit project URL.

Note that building or testing against this change will require you to
move your working directory to `$GOPATH/src/gerrit.wikimedia.org/r/blubber`.

Contribution documentation was updated to reflect the changes, and the
`.arcvendor` submodule has been removed.

Bug: T200452
Change-Id: I3ab23e420b2825e86e2bd7c9b3da9d4de23edaa1

Summary:
Change `node.dependencies` flag to `node.requirements`, the list of
files (typically `package.json` and either `npm-shrinkwrap.json` or
`package-lock.json`) that declare dependencies to be installed with NPM.

Test Plan: Run `go test ./...`. Try it out with something like Mathoid.

Reviewers: thcipriani, hashar, mobrovac, Joe, akosiaris, #release-engineering-team

Reviewed By: thcipriani, #release-engineering-team

Tags: #release-engineering-team

Differential Revision: https://phabricator.wikimedia.org/D1058

Summary:
Implemented a validation system using the
`github.com/go-playground/validator` package, extending it with custom
validation tags, and implemented translation of validation errors into
somewhat human-friendly messages.

Fixes T175186
Depends on D845

Test Plan: Run the unit tests and try running blubber against some bad config.

Reviewers: thcipriani, hashar, Jrbranaa, Joe, #release-engineering-team, mobrovac

Reviewed By: thcipriani, #release-engineering-team

Tags: #release-engineering-team

Maniphest Tasks: T175186

Differential Revision: https://phabricator.wikimedia.org/D868

Summary:
Wrote inline documentation for all the things.

Fixes T168000

Test Plan: Execute `godoc -http=:6060` and proofread all the things.

Reviewers: thcipriani, hashar, #release-engineering-team, demon

Reviewed By: thcipriani, #release-engineering-team, demon

Tags: #release-engineering-team

Maniphest Tasks: T168000

Differential Revision: https://phabricator.wikimedia.org/D841

Summary:
Now that our Phabricator instance handles `go get` requests, we can use
a path without the `.git` suffix as the canonical import path.

Test Plan: Run `go test ./...` and `go build`.

Reviewers: thcipriani, #release-engineering-team

Reviewed By: thcipriani, #release-engineering-team

Tags: #release-engineering-team

Differential Revision: https://phabricator.wikimedia.org/D780

Summary:
For `npm run` to find executables provided by external dependencies, the
`$NODE_PATH/.bin` directory must be present in `PATH`.

Depends on D769

Test Plan:
Run `go test ./...`.

Build and run Mathoid's test variant at:
  https://gerrit.wikimedia.org/r/#/c/376319/2

Reviewers: thcipriani, mobrovac, hashar, mmodell, #release-engineering-team

Reviewed By: thcipriani, mobrovac, mmodell, #release-engineering-team

Tags: #release-engineering-team

Differential Revision: https://phabricator.wikimedia.org/D770

Summary:
Define `NODE_ENV` based on the configuration and define `NODE_PATH` when
either `npm.install` or `npm.env` are true. The latter behavior is
necessary for final stages of multi-stage builds where npm modules are
not installed but the application requires node-related environment
variables to run.

Depends on D757
Ref T174626

Rename npm module/config to node

Renamed `npm` yaml entry to `node` and `NpmConfig` to `NodeConfig`.
Since we're dealing with general node builds and configuration, this
seems to make more sense.

Test Plan:
Run `go test ./...` or `arc unit`. Run blubber against at least the
`blubber.example.yaml`.

Reviewers: thcipriani, mobrovac, mmodell, #release-engineering-team

Reviewed By: thcipriani, #release-engineering-team

Tags: #release-engineering-team

Maniphest Tasks: T174626

Differential Revision: https://phabricator.wikimedia.org/D759