Allow sequences maximum length to be user configurable.

README.md

@@ -291,7 +291,12 @@ you can pass a comma-separated list of options.  Options are in the form
 `foo=bar`, or just `foo` (the latter implies a boolean option that you want
 to set `true`; it's effectively a shortcut for `foo=true`).
 
-- `sequences` -- join consecutive simple statements using the comma operator
+- `sequences` (default: true) -- join consecutive simple statements using the
+  comma operator.  May be set to a positive integer to specify the maximum number
+  of consecutive comma sequences that will be generated. If this option is set to
+  `true` then the default sequences limit is `2000`. Set option to `false` or `0`
+  to disable. On rare occasions the default sequences limit leads to very slow
+  compress times in which case a value of `20` or less is recommended.
 
 - `properties` -- rewrite property access using the dot notation, for
   example `foo["bar"] → foo.bar`