Log message:
Add bl3.mk file for lbixion.

Log message:
Import libixion-0.12.1 as math/libixion.

Ixion is a general purpose formula parser & interpreter that can
calculate multiple named targets, or "cells".

The goal of this project is to create a library for calculating
the results of formula expressions stored in multiple named targets,
or "cells". The cells can be referenced from each other, and the
library takes care of resolving their dependencies automatically
upon calculation. The caller can run the calculation routine either
in a single-threaded mode, or a multi-threaded mode. The library
also supports re-calculations where the contents of one or more
cells have been modified since the last calculation, and a partial
calculation of only the affected cells need to be calculated.