fix Array.prototype.slice() to use duk_def_prop_xxx instead of duk_put_prop_xxx
fix Array.prototype.slice(); undefined elements don't affect result length
fixes to Array built-ins (recently refactor): 'length' must always be writable, non-enumerable, and non-configurable
automatic Duktape version and current date to website build
use template spans for Duktape versiona and current date in api/guide pages
ditz issue update