handle internationalized strings on windows

## Bug Report

**Expected Behavior**
international character sets are handled in utf-16

**Actual Behavior**
when marshalling strings from c# to the native library, the character set is misinterpreted. likely due ot the use of wide string and converting to string.

## steps to reproduce:

netframework ManifestGenerator uncomment one of the lines that includes spanish language.
set a break in the Manifest.h c++/cli wrapper constructor after `Utilities::MarshalString(json, _json);`

expected: the string is properly translated
actual: the string has extra characters

**Environment**
- OS: [e.g. OSX 10.13.4, Windows 10]
- Version: [e.g. 1.0.1]