Port FlatBuffers to Go.

[rw]

Implement code generation and runtime library for Go, derived from the
Java implementation. Additionally, the test suite verifies:

• the exact bytes in the Builder buffer during object construction,
• vtable deduplication, and
• table construction, via a fuzzer derived from the C++ implementation.

[rw]

Unlike the Java version, the Go port does not overwrite data when deduplicating vtables. This is a step towards basing Builder on io.Writer, instead of a byte slice, for better generality.

[rw]

I've force-pushed some small updates: code cleanup in go_test.go and removing all unnecessary calls to panic.

[ghost]

This commit is in thru a cherry-pick.

[rw]

The cherry-picked commit is: 74d5f37

[jeroenrinzema]

@rw Are there still plans to support writing to an io.Writer instead of a byte buffer?

[rw]

@jeroenrinzema No plans for that at the moment. I think the builder algorithm prevents using an io.Writer directly (because it builds back to front). I can imagine us creating some kind of writer interface that would encapsulate the builder buffer logic, though (we could call it a BackToFrontWriter).