New CVal conversion operator for native integer conversions

This idea addresses scenarios #82 and #83.

This new operator would take the form: **`CVal(`_\_`,` _\_`)`**

Where _\_ can be of the following types:

* Object type: `Object`
* Signed integers: `SByte, Int16, Int32, Int64`
* Unsigned integers: `Byte, UInt16, UInt32, UInt64`
* Floating-Point: `Single, Double, Decimal`
* Character type: `Char`
* Any enumeration type

Note: This **excludes** type parameter types.

And _\_ can be any of the above types excluding `Object`.

Note: This **excludes** type parameter types.

The behavior is as follows:
* From Object to any valid target type, a native CLR unbox conversion shall be used.
* Between signed and unsigned integers, the bits of the integer shall be re-interpreted with the new type.
* If the destination type has more bits than the source type the result shall be [sign-extended](https://en.wikipedia.org/wiki/Sign_extension).
* If the destination type has fewer bits than the source type, the result shall truncate the excess bits.
* From any floating-point type to a signed integer type, the fractional portion of the floating-point value shall be truncated.
* For negative values this truncates "up" to zero.
* From the character type to any signed or unsigned integer type, the result shall be the Unicode 16 value of the character.
* From any signed or unsigned integer type to the character type, the result shall be the character indicated by that Unicode 16 value.
* For values larger than 16-bits, excess bits shall be truncated.
* Conversions to or from enumeration types shall behave as if those conversions were being performed to or from the underlying integer type of the enumeration.
* Conversion overflow/underflow checking is governed by the checked/unchecked settings of the project.

Open questions:
- [ ] Nullable/lifted conversions
- [ ] Conversions between Boolean and integer types
- [ ] Reconcile behavior being orthogonal to overflow/underflow settings with above behavior that truncates excess bits.