Fixed reading of layer's "mask_data" and "global_mask_info" fields
Fixed reading of "global_mask_info" and "tagged_blocks" sections
Fixed reading of layers and layer mask data
Implemented decoding of known undescribed descriptor's types. Some more may exist
Removed duplicated constants
Some TYPOs fixed
Misc additions and corrections to layers reader
Merge pull request #29 from EvgenKo423/master

Big work on the mistakes
fix tox.ini for Python 2.6
small style fix
very basic test for GH-29
test file from GH-20
switch to setuptools; simplify installation instructions
bump version to 1.0, add changelog entries
Added tag 1.0 for changeset 7371a4b40a94