Update pod spec

Update version number in source to v2.0.0

Update version number

This release really should be v1.3.0 according to semantic versioning
conventions.

Update README

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

Update tests for latest version of API

Add warnings to constraint removal convenience methods

Per a direct conversation with Apple, using these methods to "nuke" all the constraints on a view or view hierarchy and then installing a fresh set of constraints will result in disastrous performance when the Auto Layout engine/solver attempts to recalculate the view frames.

Instead, you'll want to make sure views are only reused with the same constraints (or with very small differences or changes to the constant value of the constraints).

Rename API method to be more concise

Update README now that the API supports Leading and Trailing attributes

Update behavior of recursive constraint removal method to exclude int…

…rinsic content size constraints

Expose a new method which allows ALL constraints (including intrinsic content size constraints) to be removed.