Mesa Examples code and README organization

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# Background

I am coming back to Mesa after being away for some time, so I am seeing things with semi-fresh eyes. Anyone coming to the examples repo looking for how this tool could be applied to their problem may find themselves a bit frustrated/confused.

Currently, the directory structure looks like:

- /examples
- /gis
- /rl

But the README is organized as:

- Grid Spacce
- Continuous Space
- Network
- Visualization
- GIS
- Other

# Issues

- [ ] The number of examples described in the README does not match the actual number of examples in the repo. Need to verify/add examples.
- [ ] Does the outline in README effectively categorize the existing examples such that each example can be binned to a single category?
- [ ] If so, should the examples be reorganized to match? I would recommend either moving them all into a single folder and using the main README to provide the overall organization/navigation, or using directories that match the README.
- [ ] The GIS examples are represented in the README differently (just bullet-points with example name) that the other examples (name in headers with short example description). Would it be helpful to standardize this?
- [ ] There are variations between examples that could be easily cleaned up to keep things consistent. e.g.: `Readme.md` vs `README.md`

Start by comparing the examples, gis, and rl directories with the main README's Grid Space, Continuous Space, Network, Visualization, GIS, and Other sections. Inventory missing or mismatched examples and review README.md versus Readme.md naming. Done means the chosen organization is documented, examples are consistently categorized, and README presentation is consistent.

Written by the indexing model from the issue text.