Add splits as startup arguments

Summary:
You can have use one of the following options:

______
|  |  |   -s or --split v
|__|__|

______
|_____|   -s or --split h
|_____|

______
|  |__|   -s or --split v-h
|__|__|

______
|__|  |   -s or --split vh
|__|__|

______
|__ __|   -s or --split h-v
|__|__|

______
|__|__|   -s or --split hv
|_____|

______
|__|__|   -s or --split vh--h
|__|__|

Reviewers: billiob

Differential Revision: https://phab.enlightenment.org/D1244
moar bold on terminology's man page!