Add a polyfil for ctype

This deals with #142 by adding a polyfil for the ctype functions
instead of failing an install.

The only downside for end users is that their version is slightly slower
if the run without ctype. But it does allow them to run it.

composer.json

@@ -26,7 +26,8 @@
     },
     "require": {
         "php": "^5.4 || ^7.0",
-        "paragonie/random_compat": "^1.0|^2.0"
+        "paragonie/random_compat": "^1.0|^2.0",
+        "backendtea/ctype-compat": "^0.1.0"
     },
     "require-dev": {
         "moontoast/math": "^1.1",