Use poetry for package

[rafalp]

trafficstars

With PIP 19 being released, we can safely move Ariadne to Poetry removing the need for maintaining separate requirements* files or setup.py.

TODO

• [x] Create pyproject.toml
• [ ] Add requirements using Poetry
• [ ] Remove setup.py
• [ ] Remove requirements files
• [ ] Update Travis config
• [ ] Add config for black to exclude snapshot directory

[rafalp]

@NyanKiyoshi from what I know pyproject.toml replaces setup.py altogether, with PIP 19 reading the build tool from it and following from there with poetry.

No idea yet when we will want to merge this PR. May want to wait a few months so Poetry 1.0 ships.

[nikordaris]

FWIW, I've recently abandoned Poetry to go back to requirements files because of frequent breaking changes between pip and poetry. The unexpected thing was these issues would appear at package install time in my apps. This forced my apps to downgrade pip to compatible versions until the lib got upgraded to a newer version of poetry that was compatible with the latest pip which was unacceptable for a tool I viewed as a dev only packaging convenience.

[patrys]

We're not planning to drop requirements.txt, just change the tool we use to maintain it.