add support for setting algorithm/nfactor for each pool separately, and fix bugged OpenCL thread cleanup (thread shutdown)
Change algorithm more robustly and faster, previous way was buggy
Merge remote-tracking branch 'mrbrdo/poolalgo' into poolalgo

Conflicts (resolved):
	ocl.h
	sgminer.c
core: rename default_algorithm to opt_algorithm.

... So it's easier to find when refactoring the configuration system
later on.
adding mrbrdo to AUTHORS.md for kernel hot-switching
core/misc: rename set_poolname() to set_pool_name().
config: use get_pool_name() in set_pool_algorithm() and set_pool_nfactor().
config: allow specifying per-pool algorithm with `--algorithm` instead of `--pool-algorithm`.

This will probably only work with config file, though, since it relies
on json_array_index.
misc: clarify currentpool() comment.
doc: clarify `algorithm` usage in a config file pool section.