fix typo in formula
fix documentation of simple material model
add parallel direct solver test
Merge pull request #78 from tjhei/direct_solver_test

add parallel direct solver test
add PETSc configuration and test support

This is a combination of 9 commits:
be silent about finding tests
add configuration parameter to find PETSc
We need to check if deal.II has PETSc support and add the compile flag
if we want PETSc.
write into detailed.log if we have PETSc
include PETSc string in build info on tester
add support for PETSc tests
rename USE_PETSC to ASPECT_USE_PETSC
update changelog.h
Merge pull request #77 from tjhei/petsc_configure

add PETSc configuration and test support
extract more prms from manual
manual: add section explaining benchmark compilation
add missing .prm
change to more safe escaping in .prm for manual
final batch of prms extracted from the manual
rename sol_cx.prm and improve manual
rename sol_kz prm