build: update pyproject.toml to replace setup.cfg

[jdhughes-usgs]

• update README.md
• update version to 1.2.9.dev0
• add pytest conftest.py

[codecov[bot]]

Codecov Report

Merging #134 (89b1caa) into master (2d6ca3f) will decrease coverage by 0.088%. The diff coverage is 100.000%.

@@              Coverage Diff              @@
##            master      #134       +/-   ##
=============================================
- Coverage   73.455%   73.368%   -0.088%     
=============================================
  Files           20        20               
  Lines         3432      3432               
=============================================
- Hits          2521      2518        -3     
- Misses         911       914        +3     

Impacted Files	Coverage Δ
pymake/config.py	100.000% <100.000%> (ø)

... and 1 file with indirect coverage changes