introduce SLHA convention conversion function
export helper function operating on FSMassMatrix objects
convert symmetric fermion mixings to SLHA convention
correcting TreeMasses test after commit 3fc4de
rename function and add comment on assumed mass matrix structure
src/slha_io.hpp: extend a comment
expose useful helper function MajoranaMassMatrixQ
use cheaper MajoranaMassMatrixQ instead of checking symmetry explicitly
compare speed of two SLHA mixing matrix conversion implementations

On my machine convert_symmetric_fermion_mixings_to_slha_forloop() is
faster than
convert_symmetric_fermion_mixings_to_slha_rediagonalization() by
approximately a factor 2 .
test speed for a 4x4 mass matrix (as it appears in the MSSM)
remove unused variable
Merge branch 'fix-slha-convention' into development
update ChangeLog