Version 0.1.0

Added

• Added requirements.txt to allow for an easy dependency installation.

Changed

• First public release version. Renamed project from simpy-dtn to pydtnsim.
• Adapted changelog and readme
• Switched to Travis CI .yml file (and removed gitlab CI file). The checks
  performed during the CI runs are the same.
• Updated setup.py to load long description from README.md with common
  function call

Fixed

• Corrected and cleaned up dependencies, deleted requirements.txt, added
  version value ranges for dependencies