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.

lex.ll

@@ -34,13 +34,13 @@
 %{
 
 #include "ispc.h"
-#include "decl.h"
 #include "sym.h"
 #include "util.h"
 #include "module.h"
 #include "type.h"
 #include "parse.hh"
 #include <stdlib.h>
+#include <stdint.h>
 
 static uint64_t lParseBinary(const char *ptr, SourcePos pos);
 static void lCComment(SourcePos *);