Added kwarg for custom grid line widths
add import for numpy function
fixed math for lineweights and the set_axis_style docstring
fixed default values when context=paper
ok really fixing the default grid weights for context==paper
Merge pull request #62 from phobson/custom-gridweight

Adding a kwarg to `set` for custom gridweights
Merge branch 'master' of github.com:mwaskom/seaborn into facet_grid
Merge branch 'facet_grid' of github.com:mwaskom/seaborn into facet_grid