Update FromChar tests
Fix the bug in SelectMany operator and name results res1 and res2 to avoid confusion

Previously there were two variables: res and res2. This
turned out to be problematic as it was easier to miss
a place where res was used instead of the res2.
Add tests for the FromText factory and fix a bug in it
Convert ParseComplete to ParseAll and TryParseAll with a clear meaning
Add DebuggerStepThrough attribute to the AnonymousParser.Parse
Add ZeroOrMore operator
Update validation of the ParserResult to allow zero length result at the end of the string
Copy default value of the offset parameter from the base Parser class
Extract the code of ZeroOrOne method and create OneOrMore operator out of it
Prefix in the FrmRegex factory is no longer needed since there is offset parameter
Add sample with basic XML parser