Filter rewrite

Major changes about filter and unfilter
1) Added filter other than '0'
2) All filter and unfilter functions moved to 'Filter' class instead of methods/module 
3) Part of this class compiled to Cython using '*.pxd' declaration, this replace old cython module with separate code
4) Installation also reworked using 'unimport', cythonize and compilation in setup.py instead of runtime compilation with 'pyximport'
5) Inside 'Reader', 'Writer' and 'Filter' class bytes represents with bytearray instead array of bytes. This make code significantly faster.