Logging is currently a bit of a mess in IMP as it basically output
whatever I was last interested in looking at. One way of systematizing
it would be
VERBOSE: each restraint/state should output enough information to
determine the flow through the code. For example, a restraint should
print out each term of its energy (so the energy for each pair of
particles for example).
TERSE: each restraint/state should print a constant number of lines
per evaluate call