Fix flake8 error/warning checking

Error/warning checking did not correctly parse output from flake8. This
resulted in Syntastic incorrectly displaying some warnings as errors.
Merge remote-tracking branch 'scrooloose/master'
use mix for elixir
Add highlight groups for the signs and the lines.

This allows users to customize the coloring of Syntastic's signs, and
also provides them a way to highlight the entire line using :sign's
linehl feature.  It preserves the current default behavior of using
the error and todo highlight groups if the customized ones aren't
present.  If the linehl group doesn't exist, then it's the same as not
specifying one, so no special highlighting for the line will occur.
always return list
Add support for buffer-local b:syntastic_checkers var.
Merge pull request #1 from xandox/use_mix_for_elixir

Use mix for elixir
This allows the overrides to work
remove unused function (because of 2519d83)
New checker for TeX / LaTeX: ChkTeX.
Update help file for b:syntastic_checkers
Merge pull request #532 from dbarnett/per_buffer

Add support for buffer-local b:syntastic_checkers var.
Merge pull request #537 from brendanjerwin/fix_coffeelint_options

Fix CoffeeLint parameter overrides
Typo: Check for puppet-lint, not puppet
Merge pull request #547 from docwhat/puppet-lint

Typo: Check for puppet-lint, not puppet
Fix syntax highlighting.

The variable force_highlight_callback is gone.

Highlight functions are now consistently named
SyntaxCheckers_<filetype>_<checker>_GetHighlightRegex(), and they
take precedence over highlighting based on column.
Merge pull request #540 from lcd047/chktex

New checker for TeX / LaTeX: ChkTeX.
Merge pull request #538 from joshuarh/simplify-ruby-checker

remove unused function (because of 2519d83)
Merge pull request #534 from xandox/master

Use mix for elixir if it available and vim started from project root
fix syntastic_auto_jump functionality

Previously we removed the code to automatically set the loclist and only
set it when required. This was needed because otherwise we could
interfere with other plugins that use the loclist.

Add the call to setloclist back in only if syntastic_auto_jump is set.
This will blow away the loclist every time the file is checked, but
setting syntastic_auto_jump is the users choice.

Fixes #533