Added a new config file parser.

The new config file parser has an interface that's nearly identical to
the OptionParser of optparse.

Below is a sample settings.py config file:

$ cat settings.py
import multiprocessing

if 'rendermode' not in locals():
    rendermode="lighting"

cachedir = "cache.%s.cachedir" % rendermode

procs = multiprocessing.cpu_count() - 1

world.py

@@ -103,12 +103,12 @@ class WorldRenderer(object):
     files to update. If it includes a trailing newline, it is stripped, so you
     can pass in file handles just fine.
     """
-    def __init__(self, worlddir, cachedir, chunklist=None, lighting=False, night=False, spawn=False, useBiomeData=False):
+    def __init__(self, worlddir, cachedir, chunklist=None, rendermode="normal", useBiomeData=False):
         self.worlddir = worlddir
         self.caves = False
-        self.lighting = lighting or night or spawn
-        self.night = night or spawn
-        self.spawn = spawn
+        self.lighting = rendermode in ("lighting","night","spawn")
+        self.night = rendermode in ("night","spawn")
+        self.spawn = rendermode in ("spawn",)
         self.cachedir = cachedir
         self.useBiomeData = useBiomeData