Scala working mode

[dotta]

MiMa checks for binary incompatibilities as defined by the JVM. This is very strict, and users may want to have a more Scala-centric compatibility check. Specifically, MiMa should use the Scala Pickler annotation to retrieve information that have been lost during compilation.

Example:

• Private types should not be reported as binary incompatibilities. Scalac does not always maintain private accessors in the generated bytecode.
• Addition/Removal of local methods.

This is very much related to #1.

Related tickets are #40 and #53

[dwijnand]

It has been deemed that MiMa shouldn't have a forwards and backwards-compatible unpickler (let's say for Scala 2.11-2.13 pickles). So this is out of scope.