Added limit() and offset() to Query Builder.

I get quite a few messages for support asking how to limit or offset a query. Granted the information is in the documentation, and the `take()` and `skip()` methods do sound kinda cool, but I think offering both will allow users to 'guess' the syntax and choose their own methods. This will ease the learning experience.

I felt it made sense to have the SQL terms as the 'real' methods and 'take' and 'skip' as the aliases so I swapped them around. I realise the tests are essentially covering the same code, but I added them incase someone fiddles with one of the methods later.