def of(path)
      ::File.content_type(path) || ::URI.content_type(path) || (
        t = ::MIME::Types.of(path).first and t.content_type
      )
    end
def of(path)
      ::File.content_type(path) || ::URI.content_type(path) || (
        t = ::MIME::Types.of(path).first and t.content_type
      )
    end
call-seq:
   ContentType.of(path) => aString or +nil+

 Get the MIME-Type of the file living at +path+. Either by looking
 directly into the file (requires FileMagic), or, assuming +path+
 might denote a URI, by asking the web server (via OpenURI), or
 finally by just looking at the file extension (requires MIME::Types).
 Returns +nil+ in case no decision could be made.

 NOTE: This is really only useful with the filemagic and mime-types gems
 installed.