As recommended by https://golang.org/pkg/cmd/go/internal/generate/:
To convey to humans and machine tools that code is generated,
generated source should have a line early in the file that
matches the following regular expression (in Go syntax):
^// Code generated .* DO NOT EDIT\.$
Similar to what protobufs does with its `Message` interface, introduce here such interface and create a generic `GetRootAs` method to deserialize a flatbuffer.
When creating a CreateXxx(...) method for a simple table type,
enum-type fields with a non-zero default must have an explicit
cast for the respective argument default value, because in C#,
there is an implicit cast from int to an enum only for 0.
Also, added an example of such type into the example monster_test
type, so that we test this feature.
