go-xla = gomlx/gopjrt+gomlx/stablehlo; First release, updated docs.

v0.1.0 Merge stablehlo and pjrt into go-xla.

• Merge stablehlo and pjrt into go-xla.
  • Changed install directory to .../lib/go-xla (instead of .../lib/gomlx/pjrt).
  • Removed deprecated xlabuilder.
  • Split PJRT CPU binary releases into https://github.com/gomlx/pjrt-cpu-binaries
• Installation scripts also exported as a library.
• Added "installer.AutoInstall".
• Improvements:
  • Fixed memory leaks on plugin destruction.
  • Replaced sync.Pool by GenPool: this avoids frequent unnecessary freeing of arenas.
• Align with Google style:
  • Removed github.com/janpfeifer/must dependencies
  • Removed testify dependencies