Expand api-codec types (#163)
* Add missing U* (number) types
* Missing number types & indexes
* Add H256, H512, Hash & Signature
* Add Bool, KeyValue & U8a (base)
* Fix LengthCompact encoder (with tests)
* AccountId
* AccountId toU8a
* Order imports
* Apply type aliasses, PropIndex -> ProposalIndex
* Cleanup mappers
* Add fromJSON to Type
* Spliut with Address, AccountId & AccountIndex
* Add some comments around the types
* instanceOf check
* Address can construct from AccountIndex or AccountId
* Remove Address.encode (unused)
* Allow instance of class in constructor
* Cleanup instanceof (String, Bool, H256, H512)
* AccountId/AccountIndex check around CodecU8a
* Fix unused imports
* Additional in-constructor instanceof constructions
* u8a allows hex, string or u8a inputs
* Metadata.fromJSON
* Add Header
* Allow CodecNumber to take hex/string inputs
* fromJSON uses decoder
* Remove LengthFixed (only compact used), add tests
* Some tests around Type
* Remove unused package
* PR comments
* Expand tests (and fix some bug - yay for tests)
* Rename /base -> /codec