Added postresql support for Insert to return primary key of inserted row.

Conflicts:
	Dapper.Contrib/SqlMapperExtensions.cs

Broke SqlBuilder to another assembly
Added Dapper.Rainbow (minimal ORM)
Changed nuget to distribute DLLs

allow Add to *replace* an existing template parameter in DynamicParameters, allowing for out/return/etc usage

fix 'could destabilise runtime' error if structs threw an error; also tidied up the locals and made the func return the right type