[WIP] Handling patch automatically

[RichardsonWTR]

In response to #76
This is a implementation to handle a PATCH request automatically.
This library is very powerful but having to handle a PATCH request by manually updating every field looks bad.

This PR introduces the UpdateResource method to DocumentContext as an extension method.
Method signature:

UpdateResource<TResource>(this DocumentContext ctx, Document document, TResource resourceToBeUpdated)

Which fields can be updated

Supported attributes

• DateTime
• string
• int
• float
• double (loses precision)
• ... assume others not supported

Supported Relationships

• to-one relationships
• to- many relationships

P.S:
This is just a naive implementation. Feel free to criticize and suggest alternatives.