fixed an enconding bug when checking for gs version
adds rcParam `axes.formatter.useoffset`

Addresses issue #2400

added test for axes.formatter.useoffset rcparam
fix operation order error in _spectral_helper and implement more tests to catch these sorts of problems in the future
Merge pull request #2495 from vlsd/py3gscheck

fixed an enconding bug when checking for gs version
Merge pull request #2401 from tacaswell/useoffset_rcparam

adds rcParam `axes.formatter.useoffset`
Fix typo in legend documentation
Merge pull request #2584 from magnunor/fix_legend_typo

Fix typo in legend documentation
Add capstyle and joinstyle properties to Patch.
Use projecting caps for axes spines (fixes #2542).
Add test for new spine capstyle, workaround PDF rendering errors in low-dpi tests.
Merge pull request #2544 from pwuertz/fix_2542

Fix 2542
Merge pull request #2571 from toddrjen/specfix

This fixes thee probllem brought up in the mailing list with the recent spectrum improvements