Fixed/implemented various QResources methods.

- data() is now exported and returns a Python read-only buffer object.
- (un)registerResourceData now accept buffers as arguments, and respects zeroes in the middle of data.
- Improved unit test.

tests/QtCore/resources.qrc

@@ -1,6 +1,7 @@
 <RCC>
     <qresource prefix="/">
         <file alias="quote.txt">quoteEnUS.txt</file>
+        <file alias="sample.png">sample.png</file>
     </qresource>
 </RCC>