Alternate hotfix for #108 - windows path length limitations

See #108 - the branch name says pretty much everything.

Interesting side-effects though:

 - no more non-ascii chars in class name, as the proxy parameters are hashed
 - ability to sign code with crypto-level secure asymmetric keys, if needed (not implemented, but the new interfaces allow for this feature)
 - shorter class names
 - proxy-generation bound to `ProxyManager` version (forces re-generation of proxies)
After thinking about it, I will keep the class version here: it is an implementation detail, and should be kept as un-implementable.