Port FlatBuffers to Go.

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

docs/source/GoUsage.md

@@ -0,0 +1,97 @@
+# Use in Go
+
+There's experimental support for reading FlatBuffers in Go. Generate code
+for Go with the `-g` option to `flatc`.
+
+See `go_test.go` for an example. You import the generated code, read a
+FlatBuffer binary file into a `[]byte`, which you pass to the
+`GetRootAsMonster` function:
+
+    import (
+       example "MyGame/Example"
+       flatbuffers "github.com/google/flatbuffers/go"
+
+       io/ioutil
+    )
+
+    buf, err := ioutil.ReadFile("monster.dat")
+    // handle err
+    monster := example.GetRootAsMonster(buf, 0)
+
+Now you can access values like this:
+
+    hp := monster.Hp()
+    pos := monster.Pos(nil)
+
+Note that whenever you access a new object like in the `Pos` example above,
+a new temporary accessor object gets created. If your code is very performance
+sensitive (you iterate through a lot of objects), you can replace nil with a
+pointer to a `Vec3` object you've already created. This allows
+you to reuse it across many calls and reduce the amount of object allocation
+(and thus garbage collection) your program does.
+
+To access vectors you pass an extra index to the
+vector field accessor. Then a second method with the same name suffixed
+by `Length` let's you know the number of elements you can access:
+
+    for i := 0; i < monster.InventoryLength(); i++ {
+        monster.Inventory(i) // do something here
+    }
+
+You can also construct these buffers in Go using the functions found in the
+generated code, and the FlatBufferBuilder class:
+
+    builder := flatbuffers.NewBuilder(0)
+
+Create strings:
+
+    str := builder.CreateString("MyMonster")
+
+Create a table with a struct contained therein:
+
+    example.MonsterStart(builder)
+    example.MonsterAddPos(builder, example.CreateVec3(builder, 1.0, 2.0, 3.0, 3.0, 4, 5, 6))
+    example.MonsterAddHp(builder, 80)
+    example.MonsterAddName(builder, str)
+    example.MonsterAddInventory(builder, inv)
+    example.MonsterAddTest_Type(builder, 1)
+    example.MonsterAddTest(builder, mon2)
+    example.MonsterAddTest4(builder, test4s)
+    mon := example.MonsterEnd(builder)
+
+Unlike C++, Go does not support table creation functions like 'createMonster()'.
+This is to create the buffer without
+using temporary object allocation (since the `Vec3` is an inline component of
+`Monster`, it has to be created right where it is added, whereas the name and
+the inventory are not inline).
+Structs do have convenient methods that allow you to construct them in one call.
+These also have arguments for nested structs, e.g. if a struct has a field `a`
+and a nested struct field `b` (which has fields `c` and `d`), then the arguments
+will be `a`, `c` and `d`.
+
+Vectors also use this start/end pattern to allow vectors of both scalar types
+and structs:
+
+    example.MonsterStartInventoryVector(builder, 5)
+    for i := 4; i >= 0; i-- {
+        builder.PrependByte(byte(i))
+    }
+    inv := builder.EndVector(5)
+
+The generated method 'StartInventoryVector' is provided as a convenience
+function which calls 'StartVector' with the correct element size of the vector
+type which in this case is 'ubyte' or 1 byte per vector element.
+You pass the number of elements you want to write.
+You write the elements backwards since the buffer
+is being constructed back to front.
+
+There are `Prepend` functions for all the scalar types. You use
+`PrependUOffset` for any previously constructed objects (such as other tables,
+strings, vectors). For structs, you use the appropriate `create` function
+in-line, as shown above in the `Monster` example.
+
+## Text Parsing
+
+There currently is no support for parsing text (Schema's and JSON) directly
+from Go, though you could use the C++ parser through cgo. Please see the
+C++ documentation for more on text parsing.