Use SPDX license identifier and set all files to GLP3+ to be consistent with...

Use SPDX license identifier and set all files to GLP3+ to be consistent with license headers in the source files. Exclude tests from being installed via 'pip install'. Updated version info.

Signed-off-by: Daniel Scheffler <danschef@gfz-potsdam.de>
3 jobs for v0.3.8 in 34 seconds (queued for 2 minutes and 2 seconds)
latest
Status Name Job ID Coverage
  Test
passed test_pyrsr #45296

00:00:12

77.0%
passed test_styles #45297

00:00:07

 
  Deploy
passed deploy_pypi #45298

00:00:14