ocaml: phase 1/5/6 float arithmetic +./-./*./. (+5 tests, 372 total)

Tokenizer: +. -. *. /. (with -. avoiding clash with negative float
literals). Parser table places dotted ops at int-precedence levels.
Eval routes to host SX +/-/*//. HM types them Float->Float->Float;
literal floats now infer as Float (was Int).

OCaml-style 1.5 +. 2.5 : Float works end-to-end through tokenize +
parse + eval + infer.

lib/ocaml/eval.sx

@@ -328,6 +328,10 @@
       ((= op "-")    (- lhs rhs))
       ((= op "*")    (* lhs rhs))
       ((= op "/")    (/ lhs rhs))
+      ((= op "+.")   (+ lhs rhs))
+      ((= op "-.")   (- lhs rhs))
+      ((= op "*.")   (* lhs rhs))
+      ((= op "/.")   (/ lhs rhs))
       ((= op "mod")  (mod lhs rhs))
       ((= op "%")    (mod lhs rhs))
       ((= op "**")   (pow lhs rhs))