customname

[Walter Schulze]

Just added a new feature, customname.
customname changes the generated fieldname. This is especially useful when generated methods conflict with fieldnames.

This was in response to an issue some users had:
http://code.google.com/p/gogoprotobuf/issues/detail?id=9&can=1

message C {
	optional int64 size = 1 [(gogoproto.customname) = "MySize"];
}

Will now be generated as:

type C struct {
	MySize		*int64
}