Fix package names

[05nelsonm]

😢

See 05nelsonm/encoding#124

All modules in core have the same package name, so the same issue that Craig is running into with Java9 Module split packages would occur for anyone using JPMS where core is a direct or transitive dependency, too...

This would be a major breaking change.

[05nelsonm]

Since API needs to be broken, need to think of any other things that have been put off b/c of breakage and get them in now in order to only break this shit once.