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/parser.sx

@@ -67,8 +67,12 @@
     (list "::" 6 :right)
     (list "+" 7 :left)
     (list "-" 7 :left)
+    (list "+." 7 :left)
+    (list "-." 7 :left)
     (list "*" 8 :left)
     (list "/" 8 :left)
+    (list "*." 8 :left)
+    (list "/." 8 :left)
     (list "%" 8 :left)
     (list "mod" 8 :left)
     (list "land" 8 :left)