Added global filetype configurations for convenience.

- Now you can define global configurations within your .vimrc for
  specific filetypes without worrying about autocmd evens.
  eg.) let g:vimpipe_javascript_command = 'node'
       let g:vimpipe_javascript_filetype = 'sh'

- The plugin now provides sane defaults to basic filetypes which we can
  expand and improve over time.
Merge branch 'feature/global_filetype_configs'
Fixed global configurations for filetype config