change num_examples to num_categories
More num_examples to num_categories changes

This is being done to match Carmel's changes on the pages branch
of streambed.
update title of text chart example
add hover text chart example
Merge branch 'pages' of https://github.com/plotly/documentation into pages
Merge pull request #26 from plotly/pages

change num_examples to num_categories and a couple other example edits