whitespace cleanup
use capitalized words in titles
fixup example package.xml, important changes

The important change is that catkin must be a
buildtool_depend and no a depend
adjustments to wording, extended intro

intro now include references to doc_depend and
changes to test_depend semantics
reorder list of depend tags

I did this mostly because exec_depend should come
after plain depend, since depend is a supper set
of exec_depend.
fix typo in description of doc_depend
Merge pull request #1 from wjwwood/rep-0140

While reviewing I made some small changes that I think should be made. The only important one is that the example has `<build_depend>catkin</build_depend>` and it should instead be `<buildtool_depend>catkin</buildtool_depend>`.