V0.6.0 Speed improvement; better league evaluation; entity gym support

What's Changed

• Multiple peformance improvements for vec_env by @kachayev in #30
• Add test cases by @vwxyzjn in #31
• Simplify mask implementation by @vwxyzjn in #32
• Better league convergence criterion by @vwxyzjn in #37
• Zero-copy zero-allocation shared buffer between JVM and NumPy arrays by @kachayev in #34
• Prototype quality-based match making by @vwxyzjn in #43
• Add observation and mask test cases by @vwxyzjn in #38
• Refactor league and produce better documentation by @vwxyzjn in #44
• Use submodules for static files by @vwxyzjn in #45
• Remove historic scripts by @vwxyzjn in #47
• Add end-to-end test cases by @vwxyzjn in #48
• Refactor eval script by @vwxyzjn in #49
• Add pre-commit utilities by @vwxyzjn in #46
• Log discounted returns by @vwxyzjn in #52
• Improve league DB cache and API by @vwxyzjn in #53
• Training evaluation improvement by @vwxyzjn in #54
• Introduce smaller and more efficient NN architecture by @vwxyzjn in #56
• Cosmetic updates to gridnet script by @kachayev in #62
• Transfer multiple maps support by @xluox in #66
• Prototype entity gym support by @vwxyzjn in #69

Full Changelog: v0.5.0...v0.6.0