Refactor emitter/hub.

Remove a bunch of constants.

Remove reemit from gadget/hub.
Brought back hub#republish to simplify hub#publish implementation.
Move check for MEMORY to republish.
Updated emitter API doc for removing emitting runners.
Aligned "republish" on gadget with hub.
Fixed memorized should be a list of values.
Added basic tests for republish, aka. memory.
`args.concat` -> ARRAY_PUSH.apply(args, ...).

Added some comments and spacing.
`ARRAY_PUSH` -> `.concat`
Polished hub memory test.
Fixed array::concat call.
Updated gadget tests.
No need to keep `args`
Merge pull request #140 from troopjs/feature/simplify-emit-and-hub

Refactoring the `emitter::emit` to use an event object and simplified hub implementation.