Use the file's directory as the process current working dir

rbenv uses the current working directory to set the ruby version. This
should be set to the current directory of the script (prevents many
many headaches!)
Default to the user's home directory
Merge branch 'master' of https://github.com/ideasasylum/sublime-text-2-ruby-markers into ideasasylum-master

Add current working directory for subprocess; Fixes rbenv ruby evaluation.
Refactor cwd code to work with Windows