Implement support for dynamic parameters utilizing RuntimeDefinedParameterDictionary

[lordmilko]

Issue #48

• Refactored Parameter class into abstract base class
• Implemented new Parameter types ReflectionParameter and RuntimeParameter
• Updated CommentReaderExtensions to only read XML comments from ReflectionParameter objects
• Renamed Test-DynamicParameters cmdlet to Test-NestedTypeDynamicParameters
• Implemented new test cmdlet Test-RuntimeDynamicParameters
• Implemented RuntimeDefinedDynamicParameter tests

I have tested this against my project's module which uses IDynamicParameters in a number of locations. The changes work quite well! I have attempted to follow the existing style of the XmlDoc2CmdletDoc code base; please let me know if there are any changes you would like to have implemented

[ChrisLambrou]

Hi! Many thanks for this PR. I've had a quick read through and it all looks sensible to me. Hopefully I'll be able to find time later today (I'm based in Cambridge, UK) for a more detailed examination, and then hopefully get it merged.