[shadowtext] Add text with drop shadow utilities.

init.lua

@@ -16,6 +16,7 @@ return {
     algo = require(BASE..'algo'),
     meta = require(BASE..'meta'),
     rect = require(BASE..'rect'),
+    shadowtext = require(BASE..'shadowtext')
     strings = require(BASE..'strings'),
     vec = require(BASE..'vec')
 }