Replace Codecov by Coveralls

Avoid returning ephemerides for yesterday or tomorrow

chore(deps-dev): bump codecov from 2.1.0 to 2.1.3

Bumps [codecov](https://github.com/codecov/codecov-python) from 2.1.0 to 2.1.3.
- [Release notes](https://github.com/codecov/codecov-python/releases)
- [Changelog](https://github.com/codecov/codecov-python/blob/master/CHANGELOG.md)
- [Commits](https://github.com/codecov/codecov-python/commits)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

chore(deps): bump skyfield from 1.20 to 1.21

Bumps [skyfield](https://github.com/brandon-rhodes/python-skyfield) from 1.20 to 1.21.
- [Release notes](https://github.com/brandon-rhodes/python-skyfield/releases)
- [Changelog](https://github.com/skyfielders/python-skyfield/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/brandon-rhodes/python-skyfield/commits)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

chore(deps-dev): bump codecov from 2.0.22 to 2.1.0

Bumps [codecov](https://github.com/codecov/codecov-python) from 2.0.22 to 2.1.0.
- [Release notes](https://github.com/codecov/codecov-python/releases)
- [Changelog](https://github.com/codecov/codecov-python/blob/master/CHANGELOG.md)
- [Commits](https://github.com/codecov/codecov-python/commits)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

chore(deps): bump numpy from 1.18.2 to 1.18.4

chore(deps-dev): bump pylint from 2.4.4 to 2.5.2

Bumps [numpy](https://github.com/numpy/numpy) from 1.18.2 to 1.18.4.
- [Release notes](https://github.com/numpy/numpy/releases)
- [Changelog](https://github.com/numpy/numpy/blob/master/doc/HOWTO_RELEASE.rst.txt)
- [Commits](https://github.com/numpy/numpy/compare/v1.18.2...v1.18.4)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [pylint](https://github.com/PyCQA/pylint) from 2.4.4 to 2.5.2.
- [Release notes](https://github.com/PyCQA/pylint/releases)
- [Changelog](https://github.com/PyCQA/pylint/blob/master/ChangeLog)
- [Commits](https://github.com/PyCQA/pylint/compare/pylint-2.4.4...pylint-2.5.2)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Add manpage to explain terms

Add support for translation to the PDF graph

Split Python workflow to enhance DX

Display a graph in the PDF output for the ephemerides

Show a graph instead of a table for the ephemerides in the PDF output

chore(deps): bump skyfield from 1.18 to 1.20

Bumps [skyfield](https://github.com/brandon-rhodes/python-skyfield) from 1.18 to 1.20.
- [Release notes](https://github.com/brandon-rhodes/python-skyfield/releases)
- [Changelog](https://github.com/skyfielders/python-skyfield/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/brandon-rhodes/python-skyfield/compare/1.18...1.20)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Close #79
Close #80

refactor: simplify ephemerides, remove dead code

BREAKING CHANGE: the JSON format has deeply changed to enhance its
consistency

feat: add support for relative dates on --date argument

ci: run the tests in the PRs

fix: Fix wording in the PDF output

chore(deps): bump skyfield from 1.17 to 1.18

Add support for occultations

Bumps [skyfield](https://github.com/brandon-rhodes/python-skyfield) from 1.17 to 1.18.
- [Release notes](https://github.com/brandon-rhodes/python-skyfield/releases)
- [Changelog](https://github.com/skyfielders/python-skyfield/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/brandon-rhodes/python-skyfield/compare/1.17...1.18)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Add support for environment variables for the observer's position and timezone