Use shellescape function for file paths

Thanks for this plugin!

I was having an issue running focused tests in directories with parenthesis in the path name.  I was able to fix my issue by using `shellescape` when trying to call files and change directories.  

See: http://vimdoc.sourceforge.net/htmldoc/eval.html#shellescape()

I also added some keybindings that were in the README but not the plugin