Single Hpp File - v.10.9.0

@gulrak

Breaking changes
- None
New features
- Custom template namer: see TemplatedCustomNamer. (#149)
  - This gives great flexibility
  - It also introduces the ability to run Approval Tests on machines that do not have the source code, such as when doing cross-compilation.
- Options.withNamer(): Options now has the ability to specify a custom namer.
- New Path utility class: see Path.h and Path.cpp
Bug fixes
- Calls to Approvals::verify() and related methods no longer spuriously pass if the received and approved
  filenames are identical (#178)
- TextDiffReporter no longer throws when reporting that files differ.
  - This improves the content of logs when running Approval Tests in CI builds. (#106)
- ApprovalTests.cpp's tests and examples should now never be built when used as a sub-project. (#179)
Other changes
- Added new documentation sections:
- Removed CI builds for clang and gcc < v9
- Some of our internal tests now use gulrak's filesystem. Thanks @gulrak!

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