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

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:
Ensure that `DEBIAN_FRONTEND=noninteractive` is set before injecting
`apt-get install` instructions.

Test Plan: Run unit tests.

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

Reviewed By: thcipriani, #release-engineering-team

Tags: #release-engineering-team

Differential Revision: https://phabricator.wikimedia.org/D1032

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:
Refactored build instructions to use concrete types and
`build.Instruction` as an interface instead of relying on a simple enum
and arbitrary string arguments. The formal types result in:

 1. Clearer internal data structures
 2. Partial compilation and proper argument quoting for all instructions
    moved into the common `build` package
 3. Higher order instructions like `build.RunAll` that easily reduce to
    compiler specific output

Test Plan: Run `arc unit` or `go test ./...`

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

Reviewed By: thcipriani, #release-engineering-team

Tags: #release-engineering-team

Differential Revision: https://phabricator.wikimedia.org/D741

Summary:
One of Golang's "advantages" is not quibbling over style. To this end
the `go fmt` command exists. This is the result of me running:

    find . -name '*.go' -exec go fmt {} \;

Test Plan: built package, ran tests

Reviewers: dduvall, mmodell, #release-engineering-team

Reviewed By: dduvall, mmodell, #release-engineering-team

Subscribers: hashar

Tags: #release-engineering-team

Differential Revision: https://phabricator.wikimedia.org/D694

Summary:
Now that the project is hosted on Phabricator the import URIs must be
changed.

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

Reviewed By: #release-engineering-team, demon

Tags: #release-engineering-team

Differential Revision: https://phabricator.wikimedia.org/D657

Establish phases within Docker compiler to allow providers (apt, npm,
etc.) to inject their own run/copy instructions into to the Dockerfile
compilation process while leaving the compiler agnostic to the providers
themselves.

The instructions and phases are also generalized to leave room for
alternative compilers should they be needed in the future (e.g.  aci
support via acbuild) but also as a general design constraint to leave
compiler implementation concerns out of providers.

Reorganized config type declarations.

Added `RunConfig` for declaring working directory and unprivileged
runtime user. A system for enforcing restrictions should probably be
implemented for this.

Implemented Dockerfile compiler, supporting multi-stage output in cases
whether artifacts from other variants are configured.