improved vline part of ploting in plot_types/distr.py
Merge branch 'master' of github.com:zyxue/xit
updated plot_types/grped_omega_distr.py about savefig bbox
updated plot_types/pmf.py about +/- => $\pm$
Merge branch 'master' of github.com:zyxue/xit
Merge branch 'master' of github.com:zyxue/xit
improved imap.py