Add HERE support

[dieghernan]

Following #62 , I have implemented HERE:

• Docs:
  • Single Geocode/Reverse Geocode: https://developer.here.com/documentation/geocoding-search-api/api-reference-swagger.html
  • Batch Geocode: https://developer.here.com/documentation/batch-geocoder/dev_guide/topics/introduction.html

See the checklist below:

Data

• data-raw/api_reference.R updated
• Modify R/data.R

Sandbox

• Added sandbox/query_debugging/here_test.R
• Added sandbox/reverse_queries/here_reverse.R
• Sandbox for HERE batch added
• Sandbox for HERE batch reverse added

Code

• R/utils.R - Utils added for HERE
• R/query_factory.R updated
• R/geo_methods.R updated
• R/geo.R updated
• R/reverse_geo.R updated

Batch

• R/batch_geocoding.R updated
• R/reverse_batch_geocoding.R updated

Testing

• testthat test added
• Modify regression_testing.Rmd
• Run tests included in https://github.com/jessecambon/tidygeocoder/blob/master/cran-comments.md

Misc

• Update README

About HERE batch geocoding service

Some notes on batch geocoding on HERE:

• The API is asynchronous so the process is Send POST > wait until status is completed (can be checked via GET) > Retrieve via GET. This makes the batch geocoding code a bit longer.
• When sending POST, the results returns a RequestID. This is used for the subsequent GET processes. The good point is that you can retrieve previous runs using that RequestID and skipping the POST. This has been implemented.
• Jobs are deleted after 30 days link
• Batch geocoding results are in a different format than Single results, and the fields on batch results needs to be selected via the POST request. I have selected what I consider the most relevant, but those can be modified by the user via a custom query.
• There are other bits of the code that are discretional, as seconds between GET status calls, some warnings, etc. Some feedback would be appreciated.
• HERE Batch Geocoding is really slow. It can be useful for very large requests (limit of 1,000,000 plus the possibility of retrieving previous jobs as mentioned before), but I decided to force the batch mode only if the user requests it. Note that this is not the default behaviour for the rest of batch geocoder (batch by default if n>1 and mode is not single) but from an user perspective it can be frustating to wait 1 minute for geocoding two addresses.

Glad to know your feedback, specially on the batch geocoding implementation.

Regards