Expose new generic methods to constrain different types of attributes across 2 views

- Adjust the enums of ALEdge, ALDimension, and ALAxis to be unique (and additionally to match up with their NSLayoutAttribute counterparts)
- Add new APIs that allow any combination of ALAttributes on 2 views to be constrained
- Organize the source a bit more
- Add a new example to the demo project that uses the new generic ALAttribute methods
- Bump version number to v1.1