Update 63: Debugging code generation module.

I have tested, debugged and commented the code generation module.
Notable changes to the code are as follows:
- The bool arrays tagged_items (generateSearchplan) and matched_nodes/
  matched_edges (printed in emitMainFunction) are initialised with
  calloc instead of being allocated on the stack.
- Do not emit code to test the label class if the candidate node list
  was obtained from a call to getNodesByLabel in the generated code.
- Added a second argument to emitNextMatcherCall to parameterise
  indentation.
- Values from the left_node or left_edge were not being extracted in
  some cases. This has been fixed.
- In emitNodeFromEdgeMatcher, the generated code that inspects the
  second incident node (in the case of a bidirectional edge) did not
  update the index variable with the new node index. This has been
  fixed.
- traverseEdge adds a search operation of type 'b' if its argument
  is a bidirectional edge.