BigDecimal.Parse - add support for NumberStyles

[Bykiev]

Proposal/Summary
Right now exponent notation (and some other number styles) is not supported

Rationale
decimal.Parse supports it

Criteria for success/Definition of done
Add support for NumberStyles like in decimal.Parse

[AdamWhiteHat]

Yeah, okay. That sounds like a good suggestion.
Ill try and get around to this in the next week or two.