Map editor cannot save to xml

[dangillet]

It was found out that the map editor found in tools\editor.py cannot save correctly to xml a map if the xml contains other elements than rectmap. A workaround was to include such elements using the requires tag.

[dangillet]

I propose a temporary solution working towards a better implementation. See my branch https://github.com/los-cocos/cocos/tree/tile_editor

Digging in the problem raised many questions. Do we want to be able to load a .tmx file and be able to save it to *.xml ? It's quite a challenge to do so. Do we want to be able to change the resource in any way we can think of and still be able to save as XML representation ?

At the moment, the editor sole purpose is to edit the RectMapLayer. We add or remove Tiles in the map. The RectMapLayer can save itself correctly to xml. So I decided to only update the rectmap tag in the original xml file with whatever RectMapLayer._as_xml method is providing. Any other tags like tileset, image, imagealtas, ... are left unchanged.

I have also changed a bit the way the code was structured. I found it strange that the load_tiles function would instantiate a Resource object but then parse itself the XML file to give it to the Resource file. I thought all this logic should go in the Resource class. Recognizing that there are difference behaviours between XML and TMX files, I decided to make an Abstract Base Class Resource and derive two classes XMLResource and TMXresource to implement the different behaviours.

I've made some unit tests while I was making the changes. See file utest/test_p_resource_tiles.py. As per naming convention, I used the _p_ to show that those unit tests are to be used with py.test. They are certainly not exhaustive, but helped me during the refactoring.