fix aligned bug (test/t1.py)
introduce container displayers (repr, xml, tree-view)
figure out a reasonable way to check and generate crc

 * Discovered that repeater errors are incorrect now. StrictRepeater raises
   ArrayError, GreedyRepeater and OptionalGreedyRepeater raise RangeError, and
   nobody raises RepeaterError; in fact, it's no longer defined. Should these
   be reunified?
