Added support for including anon classes multiple times per execution

[jaxwilko]

require_once will fail to load anon classes on subsequent requests. This patch adds a caching layer that allows included classes and object to he held in memory and returned as needed

[bennothommo]

@jaxwilko I reckon we don't need to treat concrete classes any differently from anonymous classes. You could probably just create a cached instance of those classes as well, then there's no need to keep checking if it's an object or not when retrieving from the cache.

[jaxwilko]

@bennothommo yeah, was just trying to reduce memory usage by holding class references rather than the objects where possible but I guess it shouldn't make a massive difference :)

[LukeTowers]

@bennothommo I'd prefer not to, it's unnecessary memory usage to avoid having to initialize a new instance. I'm fine with this approach as it is.