Support for passing keyword arguments

The protocol is changed as follow:
Those arguments must be the last line of argument
and be enclosed in a dict with the single key 'kwargs'.

For instance:

| add
| ["s p o"]
| {"kwargs": {"lifespan":10}}
| #end#

or:

| revise
| ["s p o"]
| {"kwargs": {"policy":{"method":"add"}}}
| #end#