Also squashed:
config: add log messages to set_algo() and set_nfactor().
algorithm: use set_algorithm_nfactor() when setting default nfactor in set_algorithm().
Otherwise algorithm->n defaults to 0.
P.S. Did I already mention how this could have been C++?..
Had two bugs:
1. Will not compile due to unknown algorithm_t size.
2. nfactor is set to 0 (bad calling, fix later).
So squashed two commits:
1. algorithm: move algorithm_t definition to header.
2. config: if --nfactor is specified, properly set algorithm->nfactor.
Doc in `doc/configuration.md` (has to be started sometime, no?).
Configuration function has to be lamely-named set_algo(), because
set_algorithm() is already declared in algorithm.h (prevent namespace
conflict).
algorithm has to be added as global variable due to the way the
callback is done (by CCAN/opt, which in itself is nice).
This can be cleaned up significantly by (at least) introducing a
global configuration struct, but there is no reason to do it now
just for this - better a wholesale manana.
