Add callback() and matches().
Use filter_() and matches() in where().
Use map_() and property_() in pluck().
Return bool for where style callbacks.
Add where and pluck style callbacks to count_by() tests.
Support identity() fallback in callback().
Add TODO about merging callback() with make_callback().
Modify functionality of first(), last(), initial(), and rest() to be inline with Lo-Dash v3.0.0.
Replace utils.make_callback() with utilities.callback().
Remove incorrect usage of where callback style in uniq().
Resolve circular imports.

Closes #11
Pylint.
Add memoize().