Actually use apiPath when mounting the docs

[thomasp85]

Fix #836

The apiPath option was never used during the actual mounting of the docs router - only for reporting the url of it.

This is now fixed.

@schloerke can you please advise me where tests for this bug (and the fix) are best placed?

[schloerke]

I believe this still needs to be there as the docs will want to be mounted again on a followup run.

[schloerke]

Instead of altering just the docs, should we adjust how pr$handle() and pr$mount() will prepend the path portion of

plumber/R/ui.R

Lines 12 to 22 in 5980d1e

	# Build api url
	api_url <- get_option_or_env(
	"plumber.apiURL",
	urlHost(
	scheme = get_option_or_env("plumber.apiScheme", "http"),
	host = get_option_or_env("plumber.apiHost", host),
	port = get_option_or_env("plumber.apiPort", port),
	path = get_option_or_env("plumber.apiPath", ""),
	changeHostLocation = TRUE
	)
	)

If we do not apply it internally to the two methods, we should still use the path portion of the api_url when mounting the docs.