Documentation update pass

[dshemetov]

Part of #13.

Testing the API endpoints:

• each endpoint has a link to the API docs
• most endpoints have an example call that works

Endpoints tested:

• afhsb
• cdc
• covid_hosp_facility_lookup
• covid_hosp_facility
• covid_hosp_state_timeseries
• covidcast_meta
• covidcast_nowcast (not an active endpoint yet)
• covidcast
• delphi
• dengue_nowcast (need valid locations, but API is lacking) EDIT: done in first pass endpoints vignette (for closing #96) #102
• dengue_sensors (need valid locations and names, but API is lacking) EDIT: done in first pass endpoints vignette (for closing #96) #102
• ecdc_ili EDIT: done in first pass endpoints vignette (for closing #96) #102
• flusurv
• fluview_clinical
• fluview_meta
• fluview
• gft
• ght
• kcdc_ili (need valid region, but API is lacking) EDIT: done in first pass endpoints vignette (for closing #96) #102
• meta_afhsb
• meta_norostat
• meta
• nidss_dengue
• nidss_flu
• norostat
• nowcast
• paho_dengue (bug prevents testing) EDIT: done in first pass endpoints vignette (for closing #96) #102
• quidel
• sensors
• twitter
• wiki

[brookslogan]

Note this will need a re-document() when ready. (From the checklist, it looks pretty ready; can the remaining boxes be left for another issue?)

[brookslogan]

This still needs a re-document(). And an issue to address the remaining checklist items.

[brookslogan]

Closes #50.

[brookslogan]

Looks like

• the first CI run with the updated documentation timed out trying to test the examples
• locally a check() runs fine on my system
• locally a devtools::run_examples() is currently stuck at the covid_hosp_facility_lookup example; not sure if it's going to terminate or not.

Some potential causes:

• an API hiccup
• a GitHub Action configuration issue
• a bug in the examples

[brookslogan]

Not sure how I self-requested review. The doc changes looked good when I looked them over before. The re-document() revealed an (inconsistent) issue with examples taking a long time / never terminating, maybe due to sometimes-long covid_hosp_facility_lookup run times; I'm following up on this on Slack. I think it's good to either merge or to wait for some findings regarding what's causing the inconsistent long run times. @keanmingtan would it slow you down at all to continue development off a branch split off from this PR's branch?

[brookslogan]

Trying out just marking this + another long-running example \donttest. CI checks are still going to run them, so if it's this causing them to time out, we may need to change this to something even more restrictive until the covid_hosp_facility_lookup backend performance improvements and a cmu-delphi/delphi-epidata#48 fix are out.