Add deep_get and deep_set.

Refs #32
Make has() work with deep paths and make has_path() and deep_has() aliases.

Refs #32
Revert behavior of has() so that it's not deep.
Add deep_pluck(), deep_property(), and deep_prop().

Refs #32
Make get_path() handle list indexing using strings.

Refs #32
Add deep_map_values().

Refs #32
Add docstring for deep_pluck().

Refs #32
PEP8