Eigen Memory Bugfixes

If you're a new user, don't forget to check out this section for getting started and basic usage!
The latest and strongest neural nets are still those from the former release: https://github.com/lightvector/KataGo/releases/tag/v1.4.5

A lot of recent and interesting release notes can still be found at this prior release https://github.com/lightvector/KataGo/releases/tag/v1.6.0, including basic information about the new KataGo CPU backend (eigen vs eigenavx2), and a couple of significant new features for analysis tool developers!

Changes

This is a followup release that fixes some issues with the new Eigen (CPU) implementation in 1.6.0:

• Fixed two issues that caused Eigen implementation to use massively more memory than it needed, particularly when run with many threads (which could exhaust all RAM on some systems).
• Better default settings of the numbers of threads to use in Eigen, which are now overrideable by a new separate config parameter if needed (but users should just stick to the default anyways).

And some minor other changes:

• For the analysis engine, the number of positions to search in parallel is now controlled by numAnalysisThreads in the config instead of a command line argument (but the command line argument still works, for backwards compatibility).
• The analysis engine config now allows specifying numSearchThreadsPerAnalysisThread as an alias for numSearchThreads. This is not new behavior, this is just an alias whose name hopefully conveys the effect of this parameter better.