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.
Fixed conversion of string to char[].

Fixes #287.
Added support and tests for conversions to XML.
Added support for conversions to Regex.
Added tests for conversion to enum types.
Removed unnecessary checks for null.

The base object cannot ever be null in a PSObject.
Added support and tests for PSObject.ToString().
Merge pull request #288 from ygra/more-conversions

More conversions and lots of tests