Enhance GValue error message

Change-Id: I30083ccd4abe599a65d7fe1056f6540866e81389
Use macros to simplify code

Change-Id: I5d7770ed6e12c20f90afffb502db00019b4d2866
Change macro to return value

Change-Id: I5384d51ce47512ad08d57d761c4ef3b6c1d90969
Create macro template for encoding generic asn1 structures

Change-Id: I26419f5b37032b0e0bdbbc1f3b4fb6ed8fa2bdca
Provide support for marshalling GstStructures

Change-Id: I497d175516bae5125556eb0b4f5f624978dfe639
Provide support for marshalling GstCaps

Change-Id: Ifd011c74107ac4bf32cf6d56918c844db58d4f39