Replace libdparse with DMD in UnusedParameterCheck

[Vladiwostok]

This check warns for unused function parameters, with the following exceptions:

• functions with no bodies are ignored;
• function overrides are ignored;
• parameters having only '_' chars in their name are ignored;
• parameters passed as pointers are ignored;
• parameters having 'ref' or 'out' are ignored;

This visitor inherits a common chain of visitors also used for UnusedVariableCheck (UnusedIdentifierCheck and UnusedStorageCheck. I've decided to move this check to DMD without moving it's parent classes, since most of the base class functionality is needed for the unused var check.

My approach for this visitor is:

• create a "scope" (array of AA containing some var metadata) when visiting a function;
• check the unused params in the scope only if the function should be checked;
• when visiting a Parameter, add it's metadata to the current scope;
• when visiting an identifier expression, mark the parameter as used, if it exists;
• if visiting a string expression inside a mixin statement, try to look for any of the current scope params in the string literal;
• visit '__traits' expression and mark as used the expression's arguments having the identifier type;
• when checking if a param is used, if a param is not found in the current scope, the parent scopes are checked in order to cover local function cases.

I've also added extra tests for override functions and ref / out / pointer params.
Also, the check is not 100% correct. Given the following example:

void testNested(int a)
{
	int nested(int b)
	{
		int a = 5;
		return a + b;
	}

	nested(3);
}

The libdparse visitor fails to warn for unused param 'a' in 'testNested'. I've kept the same behavior in DMD version.