Cache

[hildjj]

Add caching support. This ended up being a pretty big refactor. For one-shot uses in a large directory hierarchy, this might be slightly slower, but for the common case of processing multiple files in the same directory, this should be a big win.

[coveralls]

Pull Request Test Coverage Report for Build 3256204014

• 399 of 399 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.2%) to 99.459%

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Totals
Change from base Build 3229585848:	0.2%
Covered Lines:	647
Relevant Lines:	650

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💛 - Coveralls

[hildjj]

Still needs negative caching added.