Starting serializer overhaul.

Writing new unit tests next.
Serializer API updates.
Finished serializer rewrite.
More serializer updates.

Deleted outdated synchronous adapters and tests.
Bugfixes and tests for serializer.

Also fixed some bugs in the REST adapter.
Finished updating JSON serializer.
Updated REST adapter and tests.
Merge branch 'serializer-overhaul'
Updated builds after merge.