updates postscript plotting; updates submodules and readme

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 20.00000% with 52 lines in your changes missing coverage. Please review.

Project coverage is 53.20%. Comparing base (0f7caa5) to head (3ceb1a5). Report is 5 commits behind head on devel.

Files with missing lines	Patch %	Lines
src/specfem2D/setup_mesh.F90	3.44%	28 Missing :warning:
src/specfem2D/plot_post.F90	25.00%	18 Missing :warning:
src/specfem2D/write_postscript_snapshot.f90	54.54%	5 Missing :warning:
src/meshfem2D/repartition_coupling.f90	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## devel #1246 +/- ## ========================================== - Coverage 53.25% 53.20% -0.05% ========================================== Files 171 171 Lines 31452 31483 +31 ========================================== + Hits 16749 16751 +2 - Misses 14703 14732 +29 ``` | [Flag](https://app.codecov.io/gh/SPECFEM/specfem2d/pull/1246/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=SPECFEM) | Coverage Δ | | |---|---|---| | [](https://app.codecov.io/gh/SPECFEM/specfem2d/pull/1246/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=SPECFEM) | `?` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=SPECFEM#carryforward-flags-in-the-pull-request-comment) to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

---

🚨 Try these New Features:

• Flaky Tests Detection - Detect and resolve failed and flaky tests