Update README.md
update readme, .travis
Update README.md
Update README.md
change unsigned int to size_t
rework on node and net sturctures
tidy up code
set getter and setter for branch length
tidy up code
save changes for tidy up code
tidy up code, found bug hybrid-Lambda -spcu trees/4_tax_sp_nt1_para -o example2 -num 2 -mu 0.00003 -sim_mut_unit -sim_num_mut -mm 1.1 -seed 1410225409
merge dev