Next set of URL Checker Enhancements

- [ ] Fix URL checker not detecting redirect/login links.
ex.

```
http://www.esri.com/apps/products/download/index.cfm?fuseaction=download.main&downloadid=999999
https://github.com/orgs/Esri/teams/arcgis-defense-team/repositories
```

Note: these link should be failing but they work because a valid page is returned (a login page)
- [ ] Add ability to run script against a single file. (rather than a folder)
- [ ] Add a readme to the folder that explains how to use in a bit more detail (mainly how to set/make sure you have a server running to test the local links with)
- [ ] img src links ex: `

Start by locating the URL checker script and its containing folder, then run it against the examples in the issue with a local server available for local links. Done means redirects and login pages are detected, single-file and img src checks work, the unavailable-download text is recognized, and the folder README explains setup and usage.

Written by the indexing model from the issue text.