add save/load to param store (with some accompanying changes)

[martinjankowiak]

paramstore now has save/load. this is a simple first pass. open to suggestions for improvements.

the usage is as follows.

    # define model, run inference, etc...
    pyro.get_param_store().save('paramstore.save')
    # close session and open new session
    pyro.get_param_store().load('paramstore.save')
    # params are now in paramstore but any modules must be synced before they work
    pyro.sync_module("mymodule", pt_mymodule)
    # now good to go, as if the session had never ended...

-- removed 'tags' from paramstore
-- params from module are named using the pytorch construct and not str(id(object))
-- renamed _clear_cache() to clear()
-- serialization via cloudpickle for now
-- per_param_args for optim changed slightly
-- one unit test for save/load added

[martinjankowiak]

travis build will fail until cloudpickle added to travis environment

[jpchen]

remove these comments since its tested above

[jpchen]

looks good!

youre failing a python3 test - can you fix that ?
also probably should remove the commented code

[jpchen]

can you add an assert here just to see that clear() cleared the cache store?

[jpchen]

dont need this else

[jpchen]

add a short comment here; eventually this will be in the docs

[eb8680]

All of these dict.keys().sort() calls are invalid in Python 3, please fix.

[eb8680]

Python 3 test still failing, but otherwise LGTM.

[martinjankowiak]

added some asserts and incorporated people's suggestions.

thought i dealt with all python3 issues but strangely travis keeps complaining. i made myself a local 3.5 environment, and everything seems fine there. and when i use travis' debugging functionality and log on to the shell and run the tests manually, everything seems fine. no idea what's going on....

[eb8680]

@martinjankowiak Are you running only the param tests manually? Is it failing because of some other tests not clearing the param store?