cli: Default to reading input from stdin

See merge request !6

Add automation for CI releases

See merge request !4

* On new tag
  * ensure artifacts don't expire
  * publish a new release
  * link the packages created as artifacts

Add CI for running test suite

See merge request !1

* CI step for testing
* CI step for linting
* CI for debian/python packaging

* When input tile zoom is in maxzoom we only care about traversing parents until root
* When input tile zoom is between 0 and maxzoom we traverse both parents (up to the root) and children up to maxzoom
* When input tile zoom is 0 we traverse only children up to maxzoom
* If a tile is already discovered stop recursion