Support .ml4 files

[jfehrle]

Please treat .ml4 files (lexer input files) the same as .ml files. They seem to have the same format as .ml files, although the "[<" and ">]" in match constructions may be an extension (still learning this stuff).

An example showing [< ... >]:

  let rec loop_symb = parser
    | [< ' (' ' | '\n' | '\r' | '\t' | '"') >] -> bad_token str
    | [< s >] ->
        match unlocated lookup_utf8 Ploc.dummy s with
        | Utf8Token (_,n) -> njunk n s; loop_symb s
        | AsciiChar -> Stream.junk s; loop_symb s
        | EmptyStream -> ()

[giraud]

minimal support in 0.34

[jfehrle]

Looks much better, thanks!