Merge pull request #196 from apple/fix-incompat

Add default implementation so that existing AsyncFXKeys still work

Merge pull request #195 from swsnider/cache_fixer

Allow FXKeys to have programmatic 'cache fixing' methods

Merge pull request #192 from swsnider/hash-more

Make the action IDs more resilient to potential collisions

Merge pull request #191 from weissi/jw-more-tsc

allow more TSC versions

Fix quadratic behavior in KeyConfiguration

h/t @weissi

Fix usage not supported by older Xcode/Swift

Fix tests broken by #181

Allow prefix-matching in config keys.

This should be used sparingly, if at all, as it will be the
most frequent source of cache invalidation. It is primarily useful
in FXKeys that need to pass a subset of the configuration to some external
system, without knowing which of those keys are reasonable to forward.