add: pointers, & and * keywords

stack is now long long :sadge:

examples/ptr.pasm

@@ -0,0 +1,7 @@
+;; pointers usage example
+
+main:
+mov eax, 5
+mov a1, &eax	; move the address of eax in a1
+mov a1, *a1		; dereference a1 in a1
+end