BUG : improved input clean up in Axes.{h|v}line

 - passing in a (N, 1) shaped array as input causes the zipping to
   generate an extra dimension
 - closes #2197
 - use ravel + reshape to do shape validation + getting rid of
   extra dimension
Merge pull request #3014 from tacaswell/hline_vline_input_cleaning

BUG : improved input clean up in Axes.{h|v}line