API utils simplify life when creating or consuming APIs

Join one or more path components intelligently.

Rules:

• If any component starts with "http", all previous parts will be discarded.
• The returned path will always start with "/", except if it starts with "http".
• The returned path will never end with "/", except when ending in a protocol notation ("://") or enforced (see below)
• A trailing slash can be enforced with a final component "/"
• Empty strings are skipped

Examples:

• join("https://") -> "https://
• join("web", "rest", "2.0") -> "/web/rest/2.0"
• join("http://example.com/", "/api/", "/") -> "http://example.com/api/"