Vim: add mappings to open last buffer and edit in pwd

I was cruising through @wincent's Vim configuration to see if I could
find anything useful, and these two mappings seem like they are worth
taking for a spin.

\\ will open the previous buffer. This will allow me to easily jump back
and forth between two buffers.

\e will edit a file, starting in the same directory as the current file.
I believe this will save me typing when I want to create new files in
the current directory.