implement RUN command. Show line number in errors when in program mode.

c64/basic/cmd_run.s

@@ -0,0 +1,11 @@
+cmd_run:
+	;; XXX - Parse starting line number
+
+	;; Reset line pointer to first line of program.
+	lda basic_start_of_text_ptr+0
+	sta basic_current_line_ptr+0
+	lda basic_start_of_text_ptr+1
+	sta basic_current_line_ptr+1
+
+	;; Run it!
+	jmp basic_execute_from_current_line