[tutorial] add example code and figure for taggedFeatures
[tutorial] add taggedFeature example to tutorials.rst
[tutorial] rename of tagged example figure to match pattern
[tutorial] change literalincludes to show only selected lines
[tutorial] design principle blurb and small code snippets
[tutorial] basic intro to DataArrays
[tutorial] change layout of  the table of contents
[tutorial] appending data example
[tutorial] reduce code display, add links to example code
Merge pull request #94 from jgrewe/tutorial

more tutorial work...

sweet!