update docstrings of eigenvalue problem solvers for solver table
update docstrings of eigenvalue problem solvers for solver table

sfepy/sfepy,BubuLK/sfepy,BubuLK/sfepy,sfepy/sfepy,vlukes/sfepy,vlukes/sfepy,BubuLK/sfepy,vlukes/sfepy,rc/sfepy,rc/sfepy,sfepy/sfepy,rc/sfepy