declare versionScheme and enable MiMa

[SethTisue]

fixes #210

[SethTisue]

MiMa failures I'll need to dig into

[SethTisue]

okay so the MiMa failures are only on 2.11 and 2.12, not on 2.13.

[error]  * method enrichAsJavaIntFunction(scala.Function1)scala.Function1 in trait scala.compat.java8.Priority1FunctionConverters does not have a correspondent in current version
[error]    filter with: ProblemFilters.exclude[DirectMissingMethodProblem]("scala.compat.java8.Priority1FunctionConverters.enrichAsJavaIntFunction")
[error]  * method enrichAsJavaIntFunction(scala.Function1,scala.Predef#=:=)scala.Function1 in trait scala.compat.java8.Priority1FunctionConverters is present only in current version
[error]    filter with: ProblemFilters.exclude[ReversedMissingMethodProblem]("scala.compat.java8.Priority1FunctionConverters.enrichAsJavaIntFunction")
[error]  * method enrichAsJavaIntFunction(scala.Function1)scala.Function1 in object scala.compat.java8.FunctionConverters.package does not have a correspondent in current version
[error]    filter with: ProblemFilters.exclude[DirectMissingMethodProblem]("scala.compat.java8.FunctionConverters.package.enrichAsJavaIntFunction")
[error]  * static method enrichAsJavaIntFunction(scala.Function1)scala.Function1 in class scala.compat.java8.FunctionConverters.package does not have a correspondent in current version
[error]    filter with: ProblemFilters.exclude[DirectMissingMethodProblem]("scala.compat.java8.FunctionConverters.package.enrichAsJavaIntFunction")

[SethTisue]

I don't understand this. It seems to me we haven't touched this code.

I'm disinclined to spend my time digging into it. We're still in 0.x releases, and over at #213 we're planning on going 1.0, which means resetting binary compatibility anyway.

I'll just add an exclusion, and if it turns out this was a real problem we shouldn't have ignored, then I apologize to you, problem-experiencer-from-the-future.