more TODOs
simplify C code a bit and raise type conversion errors earlier on some boolean flags
enable doctest testing in etree module and extend some of them
require Cython 0.20 to build
use @cython.no_gc_clear decorator for Elements to get rid of double _Document ref hack
simplify some code

--HG--
extra : amend_source : 1d668bba12d0d020a9af88718a1e31e76bef3b19
add -w to CFLAGS for now because Cython generates some incorrect casts (but working code)
changelog
allow disabling -w C compiler option