Reworked the NBT and PND build script

This script no require CLI arguments. This helps to build all or only one library.
README.md updated accordingly.

README.md

@@ -89,32 +89,45 @@ Linux users must install python-xlib 0.14 (or over). It may be possible that the
 You should now be able to run MCEdit-Unified with `python mcedit.py` assuming you've installed all the dependencies correctly.
 On Linux, it is recommended to use the `mcedit.sh` shell script.
 
-## INSTALLING _nbt.pyx
+## BUILDING NBT AND PNG SUPPORT
 
-pymclevel contains a cython version of _nbt. This one is a lot faster, but has to be build manually.
-It requires cython 0.21.2 (Note: there are issues with 0.22)
+__Please, mind to adapt the following information according to your operating system!__
 
-```sh
-pip install cython==0.21.2
-```
+### DEPENDENCIES
 
-It's also worth upgrading setuptools:
+To build these libaries, you'll need _Cython 0.21_ and _setuptools_.
 
-```sh
-pip install setuptools --upgrade
-```
+First, install or update _setuptools_:
 
-With cython you should be able to build the file.
+* Download [get-pypi.py](https://bootstrap.pypa.io/get-pip.py)
+* Run it: `python pypi.py`
 
-```sh
-python setup.py develop
-```
+Then, install Cython:
 
-If no errors occured, only thing left to do is see if it worked correctly:
+`pip install cython==0.21.2`
+
+
+### SETUP SCRIPT
+
+This script is intended to be run in a shell opened in MCEdit-Unified folder.
+
+It takes arguments on the command line to work correctly.
+Invoke it like this:
+
+`python setup.py <argument> [argument [argument [...]]]`
+
+Without argument, it will fail. (And let you know...)
+
+
+Use the `all` argument to build all the libraries the script can handle.  
+The `nbt` one will build only the NBT support.  
+The `png` one will build only the PNG support.  
+The `help` one can, ehhh, help...
+
+After the NBT support is built, you can run a very simple test:
+
+`python setuptest.py`
 
-```sh
-python setuptest.py
-```
 
 ### Pocket Edition Support
 

setup.py

@@ -1,12 +1,85 @@
+import sys
+import os
+import platform
+import distutils.file_util
 from setuptools import setup
 from Cython.Build import cythonize
 
 # Output annotated .html
 import Cython.Compiler.Options
 Cython.Compiler.Options.annotate = True
 
-ext_modules = cythonize(["cpngfilters.pyx", "pymclevel/_nbt.pyx"])
+modules_map = {
+    "png": {"source": "cpngfilters.pyx",
+            "description": "Build the accelerator to work with PNG images."},
+    "nbt": {"source": "pymclevel/_nbt.pyx",
+            "description": "Build the accelerator to work with NBT data."}
+    }
+
+__help__ = """setup.py
+Build Cython extensions for MCEdit-Unified.
+
+You have to use at least one argument on the command line to build extensions.
+
+Valid arguments are:
+
+help   Print this message.
+all    Build all extensions.
+%s
+--     Makes this script send all remaing arguments to setuptool.
+
+In case setuptools commands like 'build' or 'install are given after a doule
+dash ('--'), you can expect unwanted behaviour, because the 'build_ext' and
+ '--inplace' are forced (added dynamicaly on the command line).
+""" % "\n".join(["%s    %s" % (k, v["description"]) for k, v in modules_map.items()])
+
+# Let people choose what to build.
+# If no argument is given on the command line, display help message.
+# If a wrong argument is given, break.
+if len(sys.argv) == 1:
+    print __help__
+    sys.exit(0)
+else:
+    ext_modules = []
+    args = sys.argv[1:]
+    msg = "Following extensions will be built: %s."
+    ext_list = []
+    for arg in args:
+        # Let send setuptools argument be on the command line.
+        print arg
+        if arg == '--':
+            sys.argv.remove(arg)
+            break
+        if not arg.startswith('-'):
+            if arg == 'help':
+                print __help__
+                sys.exit(0)
+            elif arg == 'all':
+                ext_list = list(modules_map.keys())
+                ext_modules = [v["source"] for v in modules_map.values()]
+            elif arg not in modules_map.keys():
+                print "'%s' is not a valid argument. Use 'help' one for information." % arg
+                sys.exit(1)
+            else:
+                src = modules_map[arg]["source"]
+                if src not in ext_modules:
+                    ext_list.append(arg)
+                    ext_modules.append(src)
+            sys.argv.remove(arg)
+    print msg % ", ".join(ext_list)
+
+sys.argv.insert(1, '--inplace')
+sys.argv.insert(1, 'build_ext')
 
 setup(
-    ext_modules=ext_modules
+    ext_modules=cythonize(ext_modules)
 )
+
+# On Linux, we want _nbt.so in pymclevel.
+if platform.system() == "Linux":
+    if os.path.isfile("_nbt.so"):
+        nbt_dest = os.path.join("pymclevel", "_nbt.so")
+        if os.path.isfile(nbt_dest):
+            os.remove(nbt_dest)
+        distutils.file_util.move_file("_nbt.so", nbt_dest)
+