rails.vim 5.1

* Modernize choice of rake task for running individual tests.
* Support gf for jbuilder partials.
* Support db/structure.sql.
* Support app/assets/ file creation (as opposed to public/).
* Highlight custom keywords in eruby and haml.
* Miscellaneous syntax highlighting additions.
* Eliminate assorted low value syntax highlighting tricks.
* Drop automatic set completefunc=syntaxcomplete#Complete.
* Improve log file syntax highlighting.
* Eliminate log file syntax folding for massive speed boost.
* Add g:rails_no_dbext to disable automatic dbext config.
* Partial forward compatibility with projectile.vim style projections.
* Fix :Rlocale with no argument.
* Fix :.Rake in a .task file.
* Fix relative directories in 'path'.
* Fix unintentional jumps into required files.
* Assorted alternate file fixes and enhancements.
* Assorted fixes to Rails app detection.
* Assorted buffer load performance improvements.