Bash: add `rand` script to give random #

Generates a random number between (by default) 0.0 and 1.0, inclusive.
Can optionally be passed one argument to set the upper bound, or two to
set both the lower and upper bounds. If all arguments are integers,
will
generate a random integer in the given range.
:q
Update Powerline config for latest version
Bash: remove old $CLASSPATH setting. Remove pyenv.
Bash: in $PS1, trim $PWD to ~40% of term width
Bash: add alias to run `find` in ~/Library

This path isn't usually searched by Spotlight/mdfind. This alias allows
us to easily search there, and also excludes lots of noisy
subdirectories (mail messages, Chrome cache, etc.) from the results.
Bash: add `whatismyip` alias to show public IP
Vim: show hidden (".*") files in NERDTree
Vim: add a bunch of BufferGator settings