major textures.py restructuring, not all textures implemented (Issue #516)

Be careful -- the build_* and transform_* functions no longer have a
blockID argument, because that made no sense.

overviewer_core/chunk.py

@@ -393,7 +393,7 @@ def generate_facemasks():
     left = Image.new("L", (24,24), 0)
     whole = Image.new("L", (24,24), 0)
     
-    toppart = textures.transform_image(white)
+    toppart = textures.transform_image_top(white)
     leftpart = textures.transform_image_side(white)
     
     # using the real PIL paste here (not alpha_over) because there is

overviewer_core/src/iterate.c

@@ -20,7 +20,6 @@
 static PyObject *textures = NULL;
 static PyObject *chunk_mod = NULL;
 static PyObject *blockmap = NULL;
-static PyObject *special_blocks = NULL;
 static PyObject *transparent_blocks = NULL;
 
 PyObject *init_chunk_render(PyObject *self, PyObject *args) {
@@ -46,9 +45,6 @@ PyObject *init_chunk_render(PyObject *self, PyObject *args) {
     blockmap = PyObject_GetAttrString(textures, "blockmap");
     if (!blockmap)
         return NULL;
-    special_blocks = PyObject_GetAttrString(textures, "special_blocks");
-    if (!special_blocks)
-        return NULL;
     transparent_blocks = PyObject_GetAttrString(textures, "transparent_blocks");
     if (!transparent_blocks)
         return NULL;