Fix byte compile warnings

 - args with underscore are known to be ignored
Partition docs
Fix terminology
Add Version and Package-Requires to files #45
Complete dash and dash-functional split

Also move functions that require Emacs 24 out of dash.el
Improve formatting of docs
Release 2.0.0
Add -union to list of highlighted symbols.
Use `comparator` instead of `predicate` for sort.
Update README