Update install script to check OSTYPE & restart

The osx_setup is only useful for OS X, so in the interest of keeping
this eventually portable for a Linux setup, check for OS X kernal using
$OSTYPE.

Most of the changes made via the OS X script require a restart to take
effect, so question the user upfront if they want to restart and then
force a restart for them.

Issue: #12
Delete reference to unused /lib/brew file

Delete reference to old /lib/brew sourcing as its not needed with the
use of Brewfile

Issue: #4
Update dotfiles logging to be more consistent

Update anything using the `e_warning` function to use `e_header` if
there is no need to warn, and instead just inform.

Issue: #11