Bigger board sizes

This is a non-regular side-release just for fun with precompiled executables for board sizes up to 29x29. However they will use more RAM and possibly be a little slower even when used to play 19x19 or smaller boards. So for best performance, one should still prefer the normal release.

The actual latest release (mostly bugfixes) is here: https://github.com/lightvector/KataGo/releases/tag/v1.6.1
And the latest major release with many release notes is here: https://github.com/lightvector/KataGo/releases/tag/v1.6.0
And the latest and strongest neural nets are still those from here: https://github.com/lightvector/KataGo/releases/tag/v1.4.5