Detect user shell as opposed to login shell.

Fixes #256.
Minor doc fix.
Installs to /usr/local/share instead of /etc/profile.d.

Fixes #257, #267.
gitignore: __pycache__
Merge pull request #321 from wting/install_to_usr_local_share

Installs to /usr/local/share instead of /etc/profile.d.
Add fish error logging.

Fixes #247.