Add todo item to author notes.
A halfway working version of bottom-up merge sort. Now to bring it home.
Defined `explode2', which gathers pairs of numbers into a new list.
First rough working version of bottom-up merge sort. More testing required.
Add better implementation mergesort which doesn't use expensive `explode'.
Change merge sort test from `length x' to `null? cdr x'.

Hopefully this is much more efficient, if we presume that `length' is
O(n) and `null? cdr' is a pointer chase.
Update procedure doc.
Removed some unnecessary generalizations.
Update with new location.
Add a gitignore.