Adding tests and implementation for isBool
Changing isBool check to depend on object type and not object class name

* Also adding two tests indicating that [NSNumber numberWithInt:1] and
  [NSNumber numberWithInt:0] (like any other NSNumber) are *not* BOOLs
  and should not be indicated as such by isBool
Merge pull request #41 from ipetkov/feature/is-bool

Adding tests and implementation for isBool
Implement drop.
Merge pull request #42 from vascoorey/development

Implement drop.
Implement zipWith.
Fix indentation.
zipWith will now work when array sizes mis-match (will zip up to the smallest array size.)
Add mising test cases for zipWith.
Style fixes. Add name to CONTRIBUTORS
Merge pull request #43 from vascoorey/development

Implement zipWith
Add specta and expecta tests
Add gitignore.
WIP: First attempt at string support. Specta tests need some improvement.
Fix capitalize.
Fix trim.
(Split) Changed split behavior to split at whitespaces. Add splitAt to specify a separator string. Tweak tests.
Removed UnderscoreSpec.m. Inlined strings into test cases for better readability.
Add split. Refactored signature of uppercase, lowercase, capitalize and trim. Add tests for all functions.
Shortened class method names (ditched the 'string' prefix).