Use extension methods on primitive types (int, string, etc) to perform the toBytes/fromBytes conversions

It would be nicer to have an interface, IAMPEncoding, that has two methods for encoding types to bytes on the wire, and decoding bytes to instances of the corresponding type.

Will implement this interface as extension methods on the primitive types themselves such as int, string, decimal, etc...

Other folks that implement their own AMP wire-level types can implement this interface so that their types will be handled by the AMP assembly correctly.