Prepare to release 2.0.0

- Modify change logs
- update requiremets
- Change version
Change version to 2.0.0
Fix notic
Merge pull request #85 from kula1922/feature/prepare-to-release

Prepare to release 2.0.0
Merge branch 'release/2.0.0' of https://github.com/allegro/ralph_pricing into release/2.0.0
Merge pull request #86 from kula1922/release/2.0.0

Release/2.0.0