Doc improvements

[d-chambers]

Description

This PR:

• Adds examples for some top-level DASCore functions
• Improves the site styling by tweaking the css
• Makes example patch functions public
• Adds a function for getting a dataframe of functions, their cross links, and descriptions.

Checklist

I have (if applicable):

• [ ] referenced the GitHub issue this PR closes.
• [ ] documented the new feature with docstrings or appropriate doc page.
• [ ] included a test. See testing guidelines.
• [ ] your name has been added to the contributors page (docs/contributors.md).
• [ ] added the "ready_for_review" tag once the PR is ready to be reviewed.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (9ade640) 99.51% compared to head (75f6528) 99.52%. Report is 1 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #335 +/- ## ========================================== + Coverage 99.51% 99.52% +0.01% ========================================== Files 92 91 -1 Lines 7170 7191 +21 ========================================== + Hits 7135 7157 +22 + Misses 35 34 -1 ``` | [Flag](https://app.codecov.io/gh/DASDAE/dascore/pull/335/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DASDAE) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/DASDAE/dascore/pull/335/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DASDAE) | `99.52% <100.00%> (+0.01%)` | :arrow_up: | 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=DASDAE#carryforward-flags-in-the-pull-request-comment) to find out more.

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