v0.8, 2019/01/18
   - switch from github to gitlab
   - some more support for PPL objects: permute_space_dimensions, Bit_Row,
     Bit_Matrix
   - upgrade gmpy2 version dependency
   - add pyproject.toml and setup.cfg files
   - remove the OK functions which caused trouble for clang on FreeBSD
   - switch back to github under SageMath organization
   - fast initialization of Linear_Expression from list/dict
   - CI (test, linter, doc build and deployment)
   - add a Cython pool for ppl.Variable
   - support for congruences
v0.7, 2017/11/24
   - use of gmpy2 for integers and rationals (Vincent Delecroix/Vincent Klein)
   - tests on travis (Vincent Delecroix/Vincent Klein)
   - fixes in install scripts (Vincent Delecroix)
   - port some upgrades from Sage (Vincent Klein)
   - split in several Cython files (Vincent Klein)
   - adding widening (Jesús Doménech)
v0.6, 2016/01/17 -- distribution bug fixes
v0.5, 2016/01/17 -- bug fixes
v0.4, 2016/01/16 -- iterator for MIP_Problem
v0.3, 2016/01/16 -- Reworked documentation
v0.2, 2016/01/16 -- Fix build
v0.1, 2016/01/16 -- Initial release