Added conversion to char according to spec.
Added tests for conversions to integer types.
Added tests for conversions to floating-point types.
Added tests for conversion to array.
Added (not working) support for conversions to XML.
Added support for conversions to Regex.
Added tests for conversion to enum types.
Added tests for PSObject.ToString().
Removed unnecessary checks for null.

The base object cannot ever be null in a PSObject.