Add OCaml code generation (#24)

Also start using nailgun to speed up code generation.

  Resolves #6.

Co-authored-by: Glen Whitney <glen@studioinfinity.org>
Reviewed-on: glen/fostr#24
Co-Authored-By: Glen Whitney <glen@nobody@nowhere.net>
Co-Committed-By: Glen Whitney <glen@nobody@nowhere.net>

tests/basic.spt

@@ -59,8 +59,8 @@ For example, this snippet generates the following Python:
 It generates nearly identical code in
 this simple example for Javascript (just with `"Hello, world!"`
 in place of `r'Hello, world!'`), although it generates a different
-preamble defining Stdio for each language. (Currently, Haskell code
-generation is also supported.)
+preamble defining Stdio for each language. (Currently, Haskell and OCaml
+code generation are also supported.)
 
 There's not much to break down in such a tiny program as this, but let's do
 it. The prefix operator `<<<` could be read as "the default stream receives...",
@@ -108,7 +108,7 @@ again. That way we can use the general (left-associative)
 parse to TopLevel(
   Gets(Gets(Gets(Gets(DefGets(LitString("'Two and '")),Int("2")),
                  LitString("' make '")),Sum(Int("2"),Int("2"))),
-       EscString("\"./n\"")))
+       EscString("\".\n\"")))
 /** writes
 Two and 2 make 4.
 **/