Expanded Makefile snippet for TDD

Has some commented code that makes the transition from startup with
everything in a single test source file to proper separation of prod and
test source
Added most of remaining gtest snippets

Snippets for most setup and teardown, header inclusion as well as
definition and registration of global test environments
Added snippets for assertion results and methods

Plus a bunch of small enhancements to existing gtest snippets
Predicate formatters for arity=1 and arity=2

Some incremental changes to other snippets
Assertion versions that use predicate formatters

Also removed "helpful" comments as to predicate format, which weren't helpful
Added helper to allow custom value printing

Aids in test failure diagnostics
Expectations and assertions for floats and doubles

Including for nearness
Merge branch 'feature/gtwrapup' into develop