SHA2HashProvider GetSalt fix, xml docs added

* SHA2HashProvider GetSalt method now returns the requested length of a
string.  Unit Tests added for GetSalt to ensure future correctness.
* CandorAuthenticationModule now accepts authentication via headers in
addition to cookies.  response headers are set with same values as auth
response cookies.  Headers have the same keys as cookies, except with
"X-" prefix.
* Added debug symbols and xml documentation