Now that I think about it, this doesn't cover some other cases.  I'll fix
those as I come across them.

Move indent related settings from syntax to index.
Fix #126

Signed-off-by: yuexin <yuecn41@gmail.com>

Also fix autolinks without angle braces which
were not being highlighted on top level.

This is accomplished by treating `>` as a comment marker.

1. Added setlocal formatoptions-=c to disable automatically inserting bullets when auto-wrapping with textwidth.
2. Added indent/mkd.vim to support auto indent in list.

Fixed an issue where `unlet b:current_syntax` occurs when recovering from a Session and b:current_syntax has not been set yet.

E.g.:

```no-highlight
bla-bla
```

Catch both numbered and unnumbered lists in a regexp pattern

Seems to fix some problems with mine. Changed so *'s and _'s inside words don't
start emphasis, which is not canonical but everyone seems to like better.

Syntax-based folding was way too slow in very large Markdown files. Add
a new file after/ftplugin/mkd.vim with a foldexpr function to determine
folds. The function is based on Steve Losh's gist at
https://gist.github.com/1038710

GFM takes three back ticks to start a code block. It can be followed with a word specifying the language. It then ends with three back ticks.
http://github.github.com/github-flavored-markdown/