Continue upgrading build tooling

[bdewilde]

changes

• migrate python packaging from setup files to equivalent pyproject.toml file
• add github actions workflow to run tests, lint, and check types; only the tests are meant to be blocking, for now
• constrains numpy package dependency to avoid an error
• bumps textacy package dependency from 0.5 to 0.10 so we can drop a transitive dependency that refused to install
  • updates call to textacy functionality that changed between versions
  • replaces one call with another package's equivalent, and adds that package to the dependencies

context

trying to move colandr forward in time in manageable chunks, from 2016 to 2020+. starting with textacy because i know it well -- i am its author :) -- with dedupe likely next. trying to save flask and its extensions until last, because that will probably be a mess.

questions

• tests aren't running in CI because of missing envvars. i'm not sure what the best solution is: create those envars in the CI env? modify the code so it doesn't require them? something else??

[bdewilde]

@samanz any thoughts on what to do about the CI testing issue? i might turn them off for now to avoid getting angry emails every commit, but would be great to get a proper CI system up and running asap.