An --ext option

[nikswamy]

From --help

 --ext One or more semicolon separated occurrences of colon-separated pairs, e.g., 'pulse:verbose;pulse:debug;foo:bar'
                These options are typically interpreted by extensions.
                An entry 'e' that is not of the form 'a:b' is treated as 'e:""', i.e., 'e' associated with the empty string

With an API in FStar.Options, which allows reading all options, or the options associated with a given extension.

val all_ext_options : unit -> list (string & string)
val ext_options (ext:string) : list string