Feature request: `autoloadkeys`, `autobrowse`

[aaaaalbert]

I request two seash modules to be written. First, autoloadkeys should inspect the current directory when seash starts, and if the dir contains exactly one keypair, it should load these keys and make them active. (This saves the user from typing loadkeys ... and as ...).

Second, autobrowse should check on startup whether there is an active keypair yet, and if so, use it to browse for vessels that this keypair can control. (This saves the user from typing browse after they have loaded their keys).

The functionalities themselves should be pretty trivial to add, but I would expect the unexpected in terms of seash startup and module initialization. If that turns out to be a big problem, we could put the two functions in one module as well.