add serializers for mutable Guava multimaps

[mtbc]

Provides serializers and accompanying tests for various Google Guava multimaps.

Does not attempt Kryo.copy support nor serialization of TreeMultimaps' comparators.

[coveralls]

Coverage increased (+1.3%) to 83.46% when pulling d31b58b on mtbc:serialize-guava-multimaps into 9a4f71e on magro:master.

[mtbc]

I'm copying the existing classes here but I'm confused: in ImmutableMapSerializer, etc., this DOES_NOT_ACCEPT_NULL is passed for Serializer's constructor's acceptsNull argument, which seems a bit backward? The names and values may need flipping, but the integration tests pass. 😕

[magro]

Haven't checked it, is this null case even tested?

[mtbc]

My tests do try serializing null values.

[magro]

Thanks for the PR! I'm currently/still on vacation, will have a deeper look at it when I'm back (in 2 weeks).

Early feedback:

• perhaps have serializers in a single java file (tests as well)?
• could you update the readme by mentioning the new serializers?

[coveralls]

Coverage increased (+1.3%) to 83.46% when pulling a04cbda on mtbc:serialize-guava-multimaps into 9a4f71e on magro:master.

[mtbc]

I think the separate base classes do a lot for reuse and decluttering, though could probably move each with default visibility into the actual file of one of their concrete extensions if that would be preferable.

No hurry on my part, enjoy your vacation and good luck with catchup afterward. 😃

[magro]

Thanks for the PR, I just released it with 0.39.

[magro]

Btw, I also just updated the kryo dependency to 4.0.0 and released kryo-serializers 0.40 with this.