Too much whitespace was getting deleted

In several places the code was using Apple's whitespace for deletable
whitespace, but it should have been using the internal
ignoreableWhitespace.
Merge pull request #619 from JasonLion/master

Too much whitespace was getting deleted
Added DTCoreTextTestCase as place for useful utilities
Added unit test for #623
added test for missing innermost /LI
corrected unit test for #623
Don't close LI if a deeper list follows,
fixes #623
Merge pull request #624 from Cocoanetics/od/issue_623

Fix for nested list output