feat: support single quote digits separator

[davidelettieri]

This PR adds support for single quote digits separator by converting into the underscore supported by C#.

Close #607

A couple of things I noticed while working on this:

• some files are missing the copyright line at the top. I added it to the new file I created but I avoided changes to other files.
• the following code is translated into a class with a private field but without initialization. If there is interest in having the initialization in the generated C# code, I'll be happy to work on the implementation.

class MyClass
{
public:
	float x = 1024;
};