LU decomposition solution works

There are slight differences between closed form and lu. But this should
not be so important.
Fixed latex error in ylabel.
Added function for counting cpu-time.
Changed duration unit to microseconds.
Added controlling through commandline

Can give flags to control program flow. Easier to get program output for
different exercises. Should work correctly but had some weird errors
where if-tests werent behaving correctly.
Mode time measuring more exact by moving measuring lines.
Merge branch 'ex-d' into development

Completed exercise d with a lot of improvements. Now finished with
developing for exactly that purpose and merging into stable version.