Change definition of $USER_BIN_HOME

A distinction is made between libraries and binaries. The home folder structure
reflects the root directory. $USER_BIN_HOME was $HOME/bin and becomes $HOME/usr.
Everything previously located in $USER_BIN_HOME is now in $USER_BIN_HOME/lib.
$USER_BIN_HOME/bin is a new folder for symlinks to binaries to exist in. This
mimics the way /usr/lib and /usr/bin work.