actions: Set up a GitHub Action for pkgdown.

pkgdown: Set up a basic GitHub Pages site.

Bump to development version 0.3.0.9000.

Expose more underlying httr parameters in push_to_gateway().

Update various links to point directly to the OpenMetrics standard.

Reset the creation time for counters when the value is reset.

Avoid using stopifnot() inside performance-sensitive methods.

Ignore CRAN-RELEASE files generated by {devtools}.

Allow register_shiny_metrics() to be called more than once.

Update the CRAN comments.

Bump to version 0.3.0 and update the NEWS file.

Move everything to the new labels API internally.

Bump roxygen version to 7.1.1.

Fix rendering of histograms with no recorded samples.

Skip Pushgateway tests when no local server is detected.