Add text_fixture::TextToBinaryTestBase::CompiledInstructions,
to more easily just examine the generated instructions by skipping
over the header.
Add spvtest::MakeInstruction utility function to easily generate
a vector containing an opcode and its operands.
Use double quotes ("). They can be interspersed with
other whitespace characters, just like shell quoting.
A backslash (\) always escapes the next character.
The end of the stream always terminates the word.
Add AutoText struct to unit test utilities, to easily
make spv_text_t values and reference them as spv_text values.
