Change format of other endpoints' doc pages to be like the covidcast endpoints

[nmdefries]

The pages should have:

• quick stats on source name, earliest issue, available geo types, license
• an introduction summarizing the contents of the data, and talking about and linking to the data source
• list of signals/fields
• table of contents
• extended info about calculation approach, limitations, backfill, missingness, source and licensing
• (new) section about supported geo-values or queries (e.g. for wiki endpoint)

Should we keep the example URLs and JSON-formatted responses? I find them not particularly useful (most users would be using our API clients) and the JSON responses take up a lot of space. Maybe keep an example API URL call, but get rid of the JSON response?

One difference between other endpoints and covidcast is that covidcast has well-defined "signals", whereas the other endpoints each return a single table with multiple signal-like columns and geo-information mixed in (e.g. for the cdc endpoint, columns are location, epiweek, num1, num2, num3, etc). Should we describe every single column (e.g. location, epiweek, num1, num2, num3), or should we only describe the signal-like columns (num1, num2, num3) since location and epiweek are expected and have a standard meaning?

Complication: the location and date columns don't always have the same names between endpoints.