add: concat for intmat, bigintmat
chg: got rid of Farey in chinrem_gcd
various changes/fixes to documentation
chg: earlier switching to dense gcd
chg: arrange variables by deg if their leading coeff has the same size
fix: error when compiling with --enable-timing
chg: leave Lucks sparse lifting earlier if input is too dense
chg: order of multiplicands if their sizes differ
chg: cut off for Karatsuba
chg: added some timing infos
chg: order of multiplicands
chg: updated test results and stats of fermat_gcd_mod_*var
chg: added more tests to factorizeQ_l