Replace magic constant test for linear solve on triangular matrices

- Provides the Skeel condition numbers `condskeel`
- Implements the error bounds derived in [JIN 5705](https://github.com/jiahao/jin/blob/master/JIN5705 - Distribution of linear algebra test failures for triangular matrices.ipynb) [(nbviewer)](http://nbviewer.ipython.org/github/jiahao/jin/blob/master/JIN5705%20-%20Distribution%20of%20linear%20algebra%20test%20failures%20for%20triangular%20matrices.ipynb?create=1)