add to twopassassembly skeleton

src/twopassassembly.c

@@ -38,3 +38,16 @@ word assembleBranch(a64inst_instruction *instr, int ){
         break;
     }
 }
+
+void firstPass(a64inst_instruction instrs[], int numInstrs){
+    //TODO:
+    // -iterate over instructions, adding to symbol table
+    // create symbol table and map labels to addresses/lines
+}
+
+void secondPass(a64inst_instruction instrs[], int numInstrs){
+    //TODO:
+    // iterate over instructions again, this time replacing labels
+    // with values from symbol table
+    // after a line has had all the values replaced, assemble it and append
+}