Fix byte-array JSValue conversions

[jasongin]

Fixes: #206

A .NET API that has a byte[] (in a property type, parameter type, or return type) should get projected as JS number[] type, not a JS string type. This change removes the conversion operators between byte[] and string-type JSValue. Since code-generation for type conversions makes use of those operators, removing those conversions achieves the desired effect of keeping the array form of the type.

In some scenarios it might actually be desirable to marshal .NET byte[] as JS string. So, it could be helpful then if there was a way for the application to control that behavior (related to #64). But I believe number[] is the most correct default.

There were a few places in test code that were relying on the implicit conversion from byte[] to JSValue; I replaced those with explicit conversions.