Fast serialize/deseriali​ze

This is an optimized rewrite of Tim Hutt's Serialize/Deserialize functions (it is up to 10x faster on arcane data structures) and supports a few additional data types.

Known limitations:
* Java objects cannot be serialized
* Arrays with more than 255 dimensions have their last dimensions clamped
* Handles to nested/scoped functions can only be deserialized when their parent functions
support the BCILAB argument reporting protocol (e.g., by using arg_define).
* New MATLAB objects need to be reasonably friendly to serialization; either they support
construction from a struct, or they support loadobj(struct), or all their important properties
can be set via set(obj,'name',value)

It has been tested relatively extensively but if you catch a bug, let me know!