plugin update ultisnips.
Ignore some specific MacVim settings.

These are loaded in MacVim's gvimrc, so we need to set these options in
vimrc, so that they are present when gvimrc's are loaded.
Add shortcut <leader>d for doc editing.
Add :Info command for useful information on the current buffer.

Since we are trying out to no longer use the airline plugin, we do need
some way of quickly accessing some useful information about the current
buffer.
Remove airline plugin.

While Airline is a nice plugin, I'm realising that all that info in the
status all of the time just isn't necessary; some basic info like file
path, file type and position in the buffer are enough when editing.

However; it _is_ necessary to be able to request more information on the
current buffer/file/directory, this is where the functions#buffer_info()
together with the :Info command come into play (see [4c6f3dd]).