Docs update

[anissa111]

See #245

This is a big one, sorry y'all. I've tried to make a comprehensive summary and explanation of all the changes.

Summary of changes

Structural

• separate environment file (build_envs/docs.yml) used for doc generation
• geocat-comp (and geocat-f2py) installation removed from settings in RTD and moved to post_create_environment step in .readthedocs.yml to circumvent default eager pip dependency update and maintain f2py namespace inclusion for docs
• theme change to book theme
• minor CSS changes for formatting of icons on "cards" on getting started and home page and minor color theming (docs/_static/style.css and docs/_static/theme_overrides.css, both included in docs/conf.py)
• start usage of docs/_static/images/logos/GeoCAT_square.svg as a favicon instead of default RTD logo
• switches notebook generation at time of docs generation off with setting nb_execution_mode = "off" in `conf.py, allows (only, for the time being) pre-rendered notebooks. Theoretically the "auto" setting would already allow this with notebooks where all cells are run, but that is not behaving as expected and is something to look into in UMBRELLA ISSUE: Migration of geocat-comp examples to this repository from geocat-examples #258

Content

• content/toctrees reorganized and removed as html links from all pages
• NSF text relocated from homepage to footer of all docs pages
• gallery style examples page
  • update_gallery() function added to docs/conf.py
  • docs/notebook_examples.txt, created when docs are generated, added to .gitignore
  • docs/gallery.yml added. Used by update_gallery() to generate notebook_examples.txt
• "Getting Started" pages added in Add "Getting Started" section to docs #240 by @hCraker
  • overview page
  • quick install page
  • mini examples page
• minor (mostly formatting or reorganization) changes for some existing content files (docs/citation.rst, docs/index.rst, docs/examples.rst)
• removal of use of ncar channel from documentation (also in Add "Getting Started" section to docs #240)
• adds rough modified first example migrated from geocat-examples, going to be cleaned up with others in UMBRELLA ISSUE: Migration of geocat-comp examples to this repository from geocat-examples #258 (needed at least one example migrated for gallery to work)
• adds toctree linkage to google forms function request form

Formatting

• addresses most of the warnings in documentation generation (that aren't coming from geocat-f2py)
  • changes links to anonymous links by switching from `text <link>`_ to `text <link>`__
  • making sure all files are properly linked in toctrees
  • minor docstring changes
• switched from :code: directive to ticks where appropriate
• some docstring changes for warning removal or for very obvious formatting issues. Will be more thoroughly addressed in Docstring improvements #259
• some changes to napoleon settings in conf.py to allow for easier type linking in docstrings (ie not having to do :class:`int` or similar anymore)

[hCraker]

This is a partial review for just the content and doc strings. I'll look at the structural RTD changes later. Thanks for doing all of this!

[hCraker]

Overall, this looks really good! I pointed out some typos and made a few suggestions.

[hCraker]

This looks great! Thank you so much!