Encpoly

Fixed

- The `decode` function no longer returns incorrect coordinates when decoding negative values (see [commit `d8b63823`]).

Added

- Further tests for the `polyline_round` function
- Tests for when encoding and decoding coordinates using a non-default precision

Changed

- Store the default precision of floating-point numbers in a module-level constant named `DEFAULT_PRECISION`

[semantic versioning]: https://semver.org/
[commit `d8b63823`]: https://github.com/JaGallup/encpoly/commit/d8b63823623303e089033468b20541bfa2a7d608