[Refactoring] Remove Statement::interpret()
[Refactoring] Remove Expression::interpret()
[Refactoring] Handle NULL Expression or Statement in interpret() call
Improve error messages in CTFE interpreter
[Refactoring] Make interpretFourPointerRelation static

Explicitly returning result from the non trivial helper function would be better than implicit result setting.
+stash for the code style changes
Interpret FuncDeclaration as a VarExp

Conflicts:
	src/interpret.c
+ok std/regex/package.d
+ok2
+ok3
Function variables ok