Christmas present to myself:  the bisect module didn't define what
happened if the new element was already in the list.  It so happens
that it inserted the new element "to the right" of all equal elements.
Since it wasn't defined, among other bad implications it was a mystery
how to use bisect to determine whether an element was already in the
list (I've seen code that *assumed* "to the right" without justification).
Added new methods bisect_left and insort_left that insert "to the left"
instead; made the old names bisect and insort aliases for the new names
bisect_right and insort_right; beefed up docstrings to explain what
these actually do; and added a std test for the bisect module.