commit in Pdata.py
1. add *args in Pdata.Pdata.plot
2. correct bug in Pdata.Pdata._check_empty_attr
3. add set_text for Pdata.Pdata
4. add mapimshow_split_axes for Pdata.Mdata
add in gnc.py 'mapbound' and 'grid' property
add **kwargs in g.plot_OLS