Improvements

[MBkkt]

Improve s2region_term_indexer:

• Add ability to reuse term buffer
• Add option for optimize index size if query only points

Add access to coverer

Add access to S2Polygon::subregionbound

Add S2_SYSTEM_HEADERS cmake options to avoid s2 compile time warnings from s2 headers

Add S2_INSTALL option with keeping old behavior

Needs tests run! PR now mostly for discussion.

[jmr]

Having 6 PRs in 1 will quickly become unwieldy. Please split up future PRs for easier disucssion.

[MBkkt]

Having 6 PRs in 1 will quickly become unwieldy. Please split up future PRs for easier disucssion.

Will be done

[smcallis]

Yeah let's split this one up we can probably submit the others separate from the term indexer one.

[MBkkt]

@jmr @smcallis Hello, I created separate PRs (found asan issue and add tests for new option) can you look they?

[jmr]

Closing this since it's been split into #298, #299, #300, #301, #302, and #303.