Fix bug in Laoutaris approximation

This commit fixes a bug that made the Laoutaris approximation fail if
run with order 3 and with parameters causing a positive discriminator
of the 3rd order equation.
Correct error message in strategy module
Remove misplaced characters from README file
Add more test cases for cache performance modelling tools

This commit adds test cases for the Lautaris cache hit ratio and the
optimal cache hit ratio calculators.