Allow multiple `registerMatchers` in one context.

The old implementation appeared to mimic that of `beforeEach` and
`afterEach`--it only allowed one per context. However, there is no need
for such a restriction when registering custom matchers. This commit
allows any number of matchers to be registered in a single context.

Other changes:

- Remove obsolete forward class declarations from KWExample header.
- Delete commented out code from KWMatcherFactory.
- Consolidate duplicated code in KWExample, KWContext in internal methods.
- Add missing variable name from block typedef (only used in
  `defineMatcher` macro).
Add tests for existing beZero matcher functionality
Make sure nil does not match beZero
Make beZero work for NSNumber as well as values
Merge pull request #447 from sgleadow/nsnumber-matcher-improvements

beZero matcher improvements for NSNumber
cleaned up
Ignore raw logs
"Merge pull request #443 from modocache/multiple-custom-matchers\n\nAllow multiple `registerMatchers` in one context."

Conflicts:
	Kiwi.xcodeproj/project.pbxproj