Open and navigate between windows

Whew! In this one, I won't go into too much detail, because I think the
code mostly speaks for itself.

My main goal here was to be able to create/delete split panes ("windows")
and navigate between them. Mostly, I just used M-x to search for
functions that do what I want, and mapped them to a <leader> key binding.

As a bonus, I made some other minor improvements:

* installed Powerline
* installed Matchit
* installed smooth-scrolling, which is a package that makes Emacs scroll
  files like Vim does, i.e. one line at a time, with a bit of runway at
  the top and bottom, instead of being all jumpy.
* enabled line truncation (don't wrap text at end of the window)

I feel good about this. I could probably start out with this on Monday
morning and be productive enough not to hate myself.

Yay Emacs!