Migration notes to 1.0.0

These notes are for those migrating from sbt-protoc < 1.0.0.

• PB.protocVersion now accepts a version in x.y.z format (for example, 3.13.0). Previously,
  this key accepted protoc-jar style version flags such as -v361. Version 1.0.x of ScalaPB will
  strip out the -v part (a behavior that will be deprecated later), however
  it does not take version numbers without dot seperators.
• Use PB.protocExecutable to use a locally installed protoc. By default
  this key downloads and caches protoc from Maven.
• If you previously used protoc-jar's option --include_std_types, see
  Installation instructions above, and look for "To make standard google.protobuf types available to import"
• Use PB.protocRun to have more control on how sbt-protoc invokes protoc (By
  default, it run PB.protocExecutable.

See CHANGELOG.md for more details.