+ Add state to the Builder object to track if we are inside a table,
  and if we are finished building the buffer.
+ Use this data to check that a buffer is being built correctly.
+ Panic if a buffer is not being built correctly.
+ Test that the panics happen as expected.

Based on d236dea1.

Also add a new `insideObject` boolean to the Builder to track whether an
object is currently being constructed. This fixes a bug with objects
that have zero fields.

Big speed boost for the typical use case of building with strings.

Change-Id: I15cc8924d6607bd93068c762fd67e6088cfd9789

Change-Id: If08b2d839489d40e977de794b13584fa66ff32c1

Add the function `Reset` to the Builder, which facilitates reuse of the
underlying byte slice.

Builder has a new CreateByteString function that writes a
null-terimnated byte slice to the buffer. This results in zero
allocations for writing strings.

This function gets around the inefficiency of populating a [ubyte] vector
byte by byte. Since ubyte vectors are probably the most commonly used type
of generic byte buffer, this seems like a worthwhile thing to create a
fast path for.

Benchmarks show a 6x improvement in throughput on x64.

There is a new test verifying the functionality of the function.

Change-Id: I82e0228ae0f815dd7ea89bf168b8c1925f3ce0d7

Change-Id: Iac5894fd8f56da7e420714558a94d63d4fea2d72

Mirrors Java patch 39d4b7e2

Change-Id: If8d0ab29f6eb508a156d468aeb0a9d5410149e53

Java patch with same purpose:
cdb0dca3

Change-Id: I57d268cc0064843779eb7812a9e69326d9ab2498
Tested: on Darwin

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.

Change-Id: Ib95a019c684891def2b50281e570b4843fea7baa