DOC link example gallery scripts rather than inline
COSMIT
DOC show referring examples on API reference pages
DOC ensure longer underline
FIX classes name in OvR
DOC mention doc-building dependency on Pillow
Merge pull request #3327 from jnothman/examples_in_apiref

DOC show referring examples on API reference pages
DOC make neural networks example appear

Also make the absence of a README fail doc compilation
DOC Fix example path
DOC fix 'Return' -> 'Returns'
FIX Py3k support for out-of-core example
DOC add links to github sourcecode in API reference
Merge pull request #3460 from jnothman/fix_nn_example_doc

[MRG+2] DOC make neural networks example appear
Merge pull request #2777 from jnothman/doc_linkcode

[MRG+2] DOC add links to github sourcecode in API reference