Reviewer suggestions

[cboettig]

Updates, as described in NEWS.md:

• Automatically detect latest release (see gbif_version()). Works with local and remote sources, can also report all available versions.
• add gbif_local() to return a remote table instead of a connection; paralleling the use of gbif_remote()
• gbif_conn() (and thus gbif_local() ) gain the ability to use arrow as a backend to duckdb, and this is now the default. This improves performance and avoids crashes when all columns are requested.
• default bucket set to "us-east-1" (across both gbif_download() and gbif_remote())
• gbif_download() now automatically detects versions, downloads parquet files to a path that parallels the remote path (using release-specific subdirectories), and allows bucket to be configured.
• set to_duckdb=TRUE by default in gbif_remote(), creating a consistent lazy-table interface with support for windowed functions
• gbif_conn() (and gbif_local()) now automatically detect the path of most recent GBIF version in gbif_dir(). No more need to to manually set path for occurrence.parquet/ subfolder.
• documentation improved.

closes #1
closes #2