Mongoframes

As Collation is now passed through the standard mongoframes import the pymongo dependency need to be updated (thanks to the TheGent for flagging this).

Added additional pymongo pass-thoughs in the base __init__ for convenience: Collation, GEOSPHERE, TEXT.

Nullify and pull now work as documented (and intended).

**New features**
- The `$sub.` projection keyword now supports for dictionaries containing list values not just dictionary values.
- New functionality added to make sort by instructions easier to define, e.g:

python
articles = Article.many(Q.published == True, sort=SortBy(Q.published_date.desc, Q.title))

Updated the setup requirements to use Faker which was renamed from fake-factory.