Add filters for unit tests; improve loader_template_paths population
Add initial support for unit testing
Add initial tests for template file creation
Remove .gitignore from twig-cache; move up
Verify filenames of compiled templates
Update wp-plugin-dev-lib 3bd5840...54d1989: Add WPCOM plugins and content from Quickstart

https://github.com/xwp/wp-plugin-dev-lib/compare/3bd5840...54d1989

54d1989 Add WPCOM plugins and content from Quickstart
Improve discovery of main plugin file for unit tests