RAFTableForm: eagerly create table, and own it

Remove -buildView and just own a tableview. Much simpler.

ref #19
Cells created eagerly: just customize during -init, no sweat

ref #19
Get rid of absolutely fucked text field configuration stuff

close #19
Provide a default (empty) model for RAFReifiedProtocol
Made it a bit easier to create validators
RAFValidator[A] ≈ A → RACSignal[RAFValidation[A]] (close #23)

This was easier than expected!
Use forall symbol in associativity law doc
Treat warnings as errors
Added RAFFunctor, super-protocol to RAFApply

Fixed fucked implementation of -[RAFValidation raf_apply:]
Added sums to RAFSemigroup, RAFMonoid; cleaned up validation signal creation
Updated README to point to RAFExamples repo (close #16)
[whitespace style]
Corrected -[RAFOrderedDictionary setObject:forKey:]
Replace elementOrdering with safe update of sections and rows arrays (+animation too)

This change is twofold; the first bit, replacing the elementOrdering block with
straight array update is simply because there's no actually need for it to be a
block, so long as forms respect object identity of their fields.

The second part is much more deep and important! Previously, updating the
elements of a form midstream was unsafe (though I didn't realize it until too
late); if the table was in the middle of a reload, its data source might change
shape underneath it, leading to lots of out-of-bounds errors and so forth. The
fix is to make the table datasources immutable: they may never change their
data. They are now called "moments" of the tableview, because that's all the
represent. A moment of the table's state. When the sections, then, of a form
change (or the rows, or any such thing), a new "moment" is generated and given
the table as its data source. We also animate these changes by diffing the
sections and rows.

The API is minimally different; the moments architecture is an implementation
detail that consumers won't be dealing with directly.
[doc fix]
Use accessor when setting editable
Fixed fucked signal creation (cruft from previous implementations, wtf)
RAFInputRow: fix import
fix sections observation
Allow API consumers to specify custom RAFTable{Form|Section}Moment subclass