Added a new enum for supported assembly syntax formats:
Canonical Assembly Format (CAF) and Assignment Assembly Format (AAF).
Updated assembler interface functions to support choice of assembly
syntax format.
Previous the api used spv_text_t and spv_binary_t for both input
and output, but depending on the usage, you either MUST
call spvBinaryDestroy or you MUST NOT call spvBinaryDestroy on the
pointer.
Always try to destroy the binary during common methods
of test fixtures. This is safe if no other code in the test
attempted to destroy the binary.
Take advantage of the fact spvBinaryDestroy is a no-op on a nullptr,
by eliminating the null pointer check in the caller.
Start using GMock: modify CMakeLists, fix googletest URL in readme.
Add useful utilities to the TestFixture class. Also make it conform to
go/gunit recommendations about setup/teardown.
