Significantly reduce the tendrils of DeclSpecs/Declarator/Declaration code

The stuff in decl.h/decl.cpp is messy, largely due to its close mapping
to C-style variable declarations.  This checkin has updated code throughout
all of the declaration statement, variable, and function code that operates
on symbols and types directly.  Thus, Decl* related stuff is now localized
to decl.h/decl.cpp and the parser.

Issue #13.

func.h

@@ -43,9 +43,7 @@
 
 class Function {
 public:
-    Function(DeclSpecs *ds, Declarator *decl, Stmt *code);
-
-    static Symbol *InitFunctionSymbol(DeclSpecs *ds, Declarator *decl);
+    Function(Symbol *sym, const std::vector<Symbol *> &args, Stmt *code);
 
     const Type *GetReturnType() const;
     const FunctionType *GetType() const;
@@ -58,10 +56,8 @@ private:
                   SourcePos firstStmtPos);
 
     Symbol *sym;
-    const FunctionType *type;
     std::vector<Symbol *> args;
     Stmt *code;
-    bool isExported;
     Symbol *maskSymbol;
     Symbol *threadIndexSym, *threadCountSym;
     Symbol *taskIndexSym, *taskCountSym;