DataSet: add utility for appending of data
DataSet.append: check for shape agreement

Fixes the Todo in the code. Based on code from @jgrewe
[test] add tests for DataSet.append
Merge pull request #79 from gicmo/data_append

DataSet: add utility for appending of data
[tutorial] some introductory words
[tutorial] add file create tutorial
[tutorial] add regularly sampled example
[tutorial] add some text the tutorials site