Follow-up: clean up in study.maths.multiangle.

Inline a method (now) only called from one place, use more modern python idioms,
add a neglected assertion.
Reworked multiangle.H in terms of an index-thirding recursion.

This saves computing most of the H[i] for i < n when computing H[n].  Also added
an assertion about a structural property constraining the square of each H(i).
Record the resistivity of copper (c/o irregular web comic).
Assorted archaic unit updates (mostly mile, informed by Wikipedia).
Record the buffer size for printing of integers.

I've now worked this out twice, so it's time to save the need to do it
again next time !
A helper tool for use with valgrind's memcheck logs.

Can parse log files, collecting reporrts of leaks and other issues.  Can iterate
over these, skipping ones marked as fixed; I can tell it when I've repaired an
error and have it mark all issues, whose stack includes a specific frame, as
fixed.  It also propagates that in some cases: when the last reader of an
uninitialized slab of memory, or last accessor of a freed slab, has been
resolved, the badly-accessed memory issue also clears itself.  This makes it
easier to keep track of which stacks still need to be fixed, as compared to
ignoring stack traces that look like ones I think I've fixed before.  There is
significant scope for further improvement here, but this is a useable first
pass.