new sfepy/base/mem_usage.py - get_mem_usage(), print_mem_usage()
add verbose argument to some routines
update parameters section in docstrings (verbose argument etc.)
new ProblemConf.update_conf(), .add_missing()
selective equations evaluation - new ProblemDefinition.eval_equations()

- update eval_equations(), Equations.evaluate() - add names argument
simplify Equations.evaluate(), update docstring
fix link in docstring of ProblemDefinition.update_materials()
update parsing lexical elements of problem configuration

- new list_dict()