Issue 506 - Addressing comments on previous few commits

[lsawade]

Description

Cosmetic changes to both code and documentation. See #506 for a full list of tasks/adjustments

• Creates documentation for most Meshfem3D structs
• Creates documentation for read_array utilities and cleans up template.
• Updates print functions
• New feature for documentation building that severely reduces build time when editing the .rst files. Until now doxygen is always run whenever you build the documentation. This should be the standard behavior. But when you are just editing the RST files and not the actual source files it causes the source xmls to be rebuilt every single time. And sphinx needs to reread the files even though nothing has changed. you can now set

  export NODOXYGEN=1

  and sphinx will check whether you want to actually rebuild the doxygen folder as well. This is not perfect, a better implementation would be through make. But I am no make wizard.
• fixes a kokkos::parallel_reduce loop to find min/max kappa and mu to run on host executionspace.

Issue Number

closes #506

Checklist

Please make sure to check developer documentation on specfem docs.

• I ran the code through pre-commit to check style
• My code passes all the integration tests
• I have added sufficient unittests to test my changes
• I have added/updated documentation for the changes I am proposing
• I have updated CMakeLists to ensure my code builds
• My code builds across all platforms

[Rohit-Kakodkar]

Thanks!

[lsawade]

Final commit fixed the NVIDIA compiler bug highlighted in #476