Version 3.1.0

Core changes:
* Added simple debug message system `:let g:syntastic_debug=1` to activate (@scrooloose)
* Added `:SyntasticInfo` command (@scrooloose)
* Refactor notifier mechanisms into notifier classes (@lcd047)
* Syntastic no longer calls `:quit` (@kovidgoyal)
* New option `g:syntastic_check_on_wq` (@lcd047)
* New option `g:syntastic_ignore_files` (@lcd047)
* New option `g:syntastic_filetype_map` (@lcd047)
* New command `:SyntasticReset` (@lcd047)
* New option `g:syntastic_aggregate_errors` (@lcd047)
* Many optimisations and speed improvements (@lcd047)
* Many bugs fixed.

Syntax checker changes:
* Added go/govet for google go (@kisielk)
* Rework of HTML/w3 (@lcd047)
* Added Python/py3kwarn for Python 3 (@liamcurry)
* Added Ruby/rubocop checker for ruby (@roktas)
* Added C/splint checker for C (@lcd047)
* Added LLVM/llvm  checker (@superjoe30)
* Added Python/pep8 checker for Python (@lcd047)
* Added nroff/mandoc checker for nroff (@lcd047)
* Added POD/podchecker checker for POD (@lcd047)
* Added C/oclint checker for C, C++, and Objective-C (@unc0)
* Added Text/atdtool spelling, style, and grammar checker (@lcd047)
* Added checkers for Objective-C++
* Added Go/golint checker for Go (@hirochachacha)
* Added COBOL/cobc checker for COBOL (@lcd047)
* Split Puppet/puppetlint into separate checkers Puppet/puppet and Puppet/puppetlint (@lcd047)
* Made the Haxe/haxe checker aware of [Vaxe](https://github.com/jdonaldson/vaxe) (@jdonaldson)
* Improved maven management for the Java/javac checher (@jvenant)
* Improved working with mix projects for Elixir/elixir (@thomas-holmes)
* Added HSS/hss checker for [HSS](http://ncannasse.fr/projects/hss) (@jdonaldson)
* Added Python/pylama checker for Python (@lcd047)
* Added Scala/fsc checker for Scala (@kongo2002)
* New options `g:syntastic_html_tidy_blocklevel_tags`, `g:syntastic_html_tidy_inline_tags`, and `g:syntastic_html_tidy_empty_tags` for the HTML/tidy checker (@anshul)
* The __gentoo-metadata__ filetype is now an alias to __xml__; the Gentoo---Metadata/xmllint still apply (@lcd047)
* Split Haskell/ghc-mod into separate checkers Haskell/ghc-mod and Haskell/hlint (@zenzike)
* Added Verilog/verilator checker for Verilog (@Kocha)
* Added AsciiDoc/asciidoc checker for AsciiDoc (@lcd047)
* Added Python/pep257 checker for Python docstrings (@marc2982)
* Many bugs fixed.