added test to find dash/hyphen with preceeding or following spaces or
both
updated regex to account for words/acronyms/numbers separated by spaces.

The regex can be refined to exclude leading and trailing spaces from the
results of pascalCaseWordBoundary.Split(). For now, word.Trim() is added
to discard the unneeded space.
added various test cases for space, dash and hyphen handling.
Removed unneccessary .Trim() from word.Length line
Removed multiple Trim()s within Select(), added a single Trim() in Aggregate()
Simplified regex by removing [\s]{0}. Updated comment to say 'underscore' instead of 'hyphen'
Updated release_notes.md with PR#341 information.
Changed the method name to highlight dealing with dashes
Merge branch 'StringExtensions'