precision by default.  If the user is OK with less precision they can change
it.

and BOBYQA.  This greatly simplifies the example.

that obviously need it.

particular, rather than just dumping exactly 400 of the last loss values, it
now dumps 400 + 10% of the loss buffer.  This way, the amount of the dump is
proportional to the steps without progress threshold.  This is better because
when the user sets the steps without progress to something larger it probably
means you need to look at more loss values to determine that we should stop,
so dumping more in that case ought to be better.

* imglab: select next/previous image with 's' and 'w'

* imglab: make 'w' and 's' keys behave like UP and DOWN keys; add 'about' text

types and put them into their own file.

Still hunting down pre-generic_image implementations

* Problem: log loss may become infinite, if g[idx] goes zero
Solution: limit the input of the log function to 1e-6 (or more)

* Parameterize the safe_log epsilon limit, and make the default value 1e-10

upper_bound_function::add().  Also fixed some issues in the solver.