release 1.0.0 on 2.12.0

[adriaanm]

• fix 2.12 compat: Provide compatibility with current Scala 2.12.x (close to RC1) #76
• bring back convenience that was lost with SD-121 Remove now-unneeded J{Function,Proc}N functional interfaces scala#5298 (we'll keep the classes in scala/scala as-is)

[adriaanm]

@szeiger, could you take the lead on getting scala-java8-compat 1.0.0 out along with 2.12?

@retronym, please add your suggestions on how to proceed to my todo list above (my meeting notes were a bit sketchy)

[szeiger]

Moving JFunction and related classes back into scala-java8-compat: #78