Remove old fasd link
Update powerline scripts to be executable

And update the invocation of them from the tmux config. This doesn't
appear to fix the issue when I test it locally. May reinstall to see.
Install powerline using pip
Update tmux configuration as instructed

https://powerline.readthedocs.org/en/latest/usage/other.html#tmux-statusline
Update tmux configuration again

Now it's not installing into the home folder, the path must change. This
path seems pretty brittle to me, but don't really have a better way
right now.