add coverage tool directory to gitignore
support iteration in CastHistory

Wing IDE debugger complains that it can't estimate the size of this
object because it doesn't have an iterator, presumably it's expecting
one to exist because CastHistory implements __len__().  Adding
__iter__() turns off this complaint.
don't use global constants for time limit and num targets, pass them instead.
complete initial implementation by revamping breeding, mutation and core algorithms

This is the completed implementation of the single-threaded version that
can serially run any specified number of populations. Its output has
been verified against the branch-and-bound algorithms for single and
multiple target encounters up to 14 seconds (after which
branch-and-bound starts to take too long to execute).
add tests of picking and breeding for genetic algorithm