Delete powerline-shell as a submodule.
Squashed 'powerline-shell/' content from commit b9478c8

git-subtree-dir: powerline-shell
git-subtree-split: b9478c882df207b6df4bb4b24a711a4be28689f6
Merge commit 'f0ce990c42ea1066d1d17f8676ce5437078523fa' as 'powerline-shell'
Add installed shell files for easier installation.
Add direnv to instructions.