previously the orthogonality check has been skipped for generalized EVP

matrix-matrix multiplication restricted to work only with actually
computed nev eigenvectors

Fix some typos in the documentation and examples

See merge request !6

instead, blacs context has to be set beforehand

if not using Hermitian multiply

Added C interface for generalized eigen problem
Extended the functionality of test.c to check generalized eigenproblem,
both with and without already decomposed matrix