Created classfor() macro

Created a super-cool `classfor()` macro which turns a class identifier into the `Class` pointer-type for the given class.

The intent here is to avoid the odd-looking `[… class]` and `….class` we all we want is the Class from a given static identifier (not the class for a given instance, which is something that a obj-c call to `class` makes sense for).  Additionally, I'd like to try to improve efficiency and compile-time safety where possible (also to satisfy my own distaste of something like this not being part of the Objective-C language).

Danger: Will exit hard and fast (at runtime) in DEBUG, due to use of getRequiredClass.
Converted existing calls to classfor()

Converted existings calls of the forms `[«class identifier» class]` and `«class identifier».class` to `classfor(«class identifier»)`.
Minor (yet crashing) typo in SceneForCG#circleEdgeColor

Fixed a minor typo in SceneForCG#circleEdgeColor; `sCircleFillColor` was being referenced instead of `sCircleEdgeColor`.  Fixes crash during rendering when switched over to CoreGraphics mode.
Checking in all Pods/*

Decided to check in all files under the Pods directory; although everything should keep working without these, it's a pain to have to run `pod install` every time I change branches with differing (unmerged) pod configurations.

Also:
• Removed Pods-related gitignores.
• Updated README.md's build instructions.