cameo: various scanner and parser fixes

- README, lang.y: changed depth parameter of "z" command to position
  (sign changes)
- lang.l: defer FILENAME after "gerber" and "gnuplot", so that we don't
  mis-read the number
- lang.l, lang.y: return the reference point after "align" as new token
  REF, not as NUMEBER, so that we can catch syntax errors that would
  cause scanner and parser to become unsynchronized
- lang.l: accept negative numbers
- lang.l: added support for comments beginning with #

cameo/lang.y

@@ -118,7 +118,7 @@ static void align(int ref, double x, double y)
 %token		TOK_GERBER TOK_GNUPLOT TOK_WRITE
 %token		TOK_DOG
 
-%token	<num>	NUMBER
+%token	<num>	NUMBER REF
 %token	<str>	STRING
 
 %type	<str>	opt_filename
@@ -130,11 +130,11 @@ all:
 	;
 
 command:
-	TOK_ALIGN NUMBER NUMBER NUMBER
+	TOK_ALIGN REF NUMBER NUMBER
 		{
 			align((int) $2, $3, $4);
 		}
-	| TOK_ALIGN NUMBER NUMBER NUMBER NUMBER NUMBER
+	| TOK_ALIGN REF NUMBER NUMBER NUMBER NUMBER
 		{
 			int ref = $2;
 			double x, y;
@@ -179,11 +179,11 @@ command:
 		}
 	| TOK_Z NUMBER
 		{
-			zo -= $2;
+			zo += $2;
 		}
 	| TOK_Z NUMBER NUMBER
 		{
-			zo -= $2+$3;
+			zo += $3-$2;
 		}
 	| TOK_GERBER NUMBER opt_filename
 		{