Started working on io package.
Merge branch 'master' into io-package
Removed Writer::append(). Added a new ResourceMap type.
Correctly type hint the bundle interface.
Started adding io tests.
Merge from master.
Fixed generics and type checker issues. Refactored Reader and Writer to be compatible.
Move type aliases around.
Removed the MoReader.
Fix tests for vector changes.
Rework HeaderBag. Fix generics.
Fixed HeaderBag tests.
Updated and fixed FileSystemStorage tests.
Final polish.
Added basic writer tests.
Added Xml and Yaml writer tests.
Merge pull request #43 from milesj/io-package

IO Package