api: draft build-mode API

[timbray]

Open for comments, please pile on.

[timbray]

Hey @jsmorph you still around? Check the changes in this draft, also #530. I've got a much bigger PR cooking that will actually implement this, including the DFA conversion. Turns out this is going to change the requirements for the LiveStorage type because unless I'm missing something it's gong to have to remember the BuildMode for each pattern and restore them in the same order they were applied. Which is enough of a semantic change that maybe we need a new OrderedLiveStorage type or suchlike. Anyhow, would appreciate your thoughts on the matter before I dive in and start changing things.

[timbray]

Further thoughts. I think we do need a LivePatterns2 class that stores either pairs of patterns/BuildMode or something logically equivalent then a Pruner2 which differs only in using a LivePatterns2. Then SetMatcherBuildMode() will check whether the current Matcher is either a coreMatcher or Pruner2 and refuse to proceed if otherwise.

[timbray]

Hah, cancel the concern. The WithPatternStorage() option is not implemented, and the docs say so. So we can just change the implementation.

[timbray]

Superseded by #543