Cesium repo commit access

Some of this has been discussed and basically agreed upon, but I wanted to explicitly mention what I think our strategy should be for granting folks commit access to the main Cesium repo.

There are three reasons to grant commit access.

  1. The contributor has expertise in significant areas of the code, so having commit access allows them to service pull requests.
  2. The contributor contributes so often that working on a fork is a, perhaps minor, pain.
  3. The contributor has contributed so much that they simply earned it.
    For more info, checkout how Subversion was ran.