Version 3.3.0

Core changes:
- Overhaul of the checker infrastructure (@lcd047)
- More detailed debugging (@lcd047)
- New command :SyntasticSetLoclist (@lcd047)
- :SyntasticCheck now accepts multiple parameters (@lcd047)
- :SyntasticInfo now takes an optional argument (@lcd047)
- Option syntastic_quiet_warnings is now deprecated (@lcd047)
- New options syntastic_quiet_messages and syntastic_<filetype>_<checker>_quiet_messages (@lcd047)
- Speed optimisations (@lcd047)
- Various bugs have been fixed.


Syntax Checker Changes
- Added cppcheck checker for C/C++ (@lcd047)
- Added eslint checker for JavaScript (@maksimr)
- Added yamlxs checker for YAML (@colinmkeith)
- Added msgfmt checker for .po files (@syucream)
- Added limbo checker for Limbo (@powerman)
- Added racket checker for Racket (@2sb18)
- Added flex checker for Lex (@lcd047)
- Added bison checker for YACC (@lcd047)
- Added mxmlc checker for ActionScript (@andyearnshaw)
- Added cgc checker for GLSL (@jrahm)
- Added rstcheck checker for reStructuredText (@myint)
- Added gotype checker for Go (@neeee)
- Added haml_lint checker for HAML (@sds)
- Rework of the python checker (@lcd047)
- New command :SyntasticJavacEditConfig for javac (@troydm)
- Added language_check grammar checker (@myint)
- Added jscs checker for JavaScript (@lcd047)
- Various bugs have been fixed.