- switch to "project authors" style copyright. Instead of an AUTHORS
file (https://opensource.google/docs/releasing/authors/), I just list
Google as a major copyright holder in the README.
- use SPDX style license headers in source files
- remove CLA requirement from contributing docs
this is an optional feature which is disabled by default, since it is
only needed in a few select cases and risks accidentally exposing
internal URLs.
Fixes#216
use consistent values for url and key and similar calling styles
(passing values as command line arguments. Also use more utilities from
the language standard library, such as java.util.Base64.