V 1.5.9 Yet Another Sparrow

Apart from the new list of helpers, there is little visible change for most users, but the command line has now been greatly extended.

Full details are in doc/Yoshimi_1.5.9_features.txt

Also, there have been significant changes in the underlying code. These were always planned, but maybe not reported and explained as well as they could have been.

More info is in dev_notes/Selection_Structure.txt

As usual, there still is much to do, but progress is steady.
