Makefile corrections, formula simplification

Remove unneeded linking flag -lstdc++ from the Makefile. Simplify the
fibonacci algorithm using the closed formula by dropping the last term
und rounding the result instead.
Correct the wording of a comment

union matrix -> identity matrix
Add wall time measurement utility

Add a wall time measurement class named ClockUtility. This is used to
simulate the behaviour of a stopwatch, including functions to start,
stop, and get the time difference between two measuring points. It makes
use of high_precision_clock frsm the new C++ 11 standard and thus
requires a new compile flag (-std=c++11).
Wall time measuring

Add Measurements class used to control and execute the time measuring,
keeping track of the results and writing back the results into a given
file. Add ResultWriter class used to write the results passed from
the Measurements class. Implement a program measuring and writing the
wall clock time of all of the implemented fibonacci functions into
files.