IEnumerable serialization / deserialization

[evolutional]

Investigate a strategy to serialize IEnumerable types. FlatBuffers currently requires knowledge of the vector item count up front for padding purposes.

It should be possible to modify the FlatBufferBuilder type in the base flatbuffers project to support writing of vectors without knowledge of the count until the end, however this would need to be pushed into the main google project first.

It may be possible to implement this functionality as an extension method, too.