Updates to `get_event()` and `get_region_id()` and various documentation improvements

[tclavelle]

This PR merges the first round of improvements to main following the initial release of gfwr. It includes the following:

• Makes get_event() dramatically faster while also handling zero-length responses without error
• Updates get_region_id() to accept aregion_id` value in addition to a region name
• Various documentation improvements to get_event(), get_region_id(), and get_raster()

[tclavelle]

New features:

• In addition to your own JSON region, can now pass EEZ or MPA id to get_raster function to query specific region

• get_region_id now takes id and returns label. This allows you to get the label for the id values returned by certain endpoints (e.g. get_event)

• Considerable speed increases in get_event function

Bug fixes:

• get_event prints "Your request returned zero results" and returns NULL when the API response contains no results instead of causing an error.

Other news:

Updated documentation

• get_raster: requires group_by and appropriate parameter name is gearType

• Added a NEWS.md file to track changes to the package.