Merge branch 'WIP_tut'
DOC: Better narrative for DBSCAN

Thanks to Robert Layton
DOC: finish misc in tutorial

@jaquesgrobler : there were still a few things to do :)
BUG: no plotting in doctests
COSMIT: layout tweak
Redo CSS layout killed by commut 94088b81
BUG: fix doctests
point out scalability problem with large numbers of classes;
use ``n_classes`` instead of ``K``
cosmit; mention scalability issues w.r.t. large number of classes
COSMIT Typo
Turned on final test (it works!)
Broadcasting used to remove a loop
Removed asserts in code
Test use assert_array_equal where appropriate
pyflakes on test
Update to documentation
Moved to the `neighbors` namespace
Example of nearest neighbor, getting an improvement when using a shrink threshold of 0.1
Explain example in docs
fix: convert input arrays to float