Correct usage of power

Element wise power '.^' instead of power '^'
New file: OCompliance

Objective function for compliance and it's first order derivative with
respect to x
Update .gitignore

Ignore testfiles
Updated E*.m

Correct see also references in help section
New file: OptOC2

Optimization function based on the optimality criteria method. The
function works in 2D.
Update: OCompliance.m

Minor correction of error message.
New file: ex1_OC2_mbb.m

Example 1 - topology optimization of a MBB beam using the OC-method.
Update README.md

Added description of the filterfunctions