#353: stab at branch exploring
add refs caching as per @Carreau's comments
removing ref caching (to be handled later)
moving full ref url building to handler (other providers), css
install IPython 2.x in docker image

allows nbviewer to render v4 notebooks
Merge pull request #362 from minrk/2.x

install IPython 2.x in docker image
add missing RUN
fix installation of IPython 2.x

pip install git+... doesn\'t get submodules right for 2.x
add numerical PDE solver example
Merge pull request #364 from waltherg/master

Add example that demonstrates how notebooks can be used to derive and implement numerical algorithms
Link to developer.rackspace.com when linking RS
Merge pull request #365 from rgbkrk/rackspace_link

Link to developer.rackspace.com when linking Rackspace
update bokeh link to new repository
Merge pull request #366 from chdoig/patch-1

update bokeh link to new repository
Added Gitter badge
Merge pull request #367 from gitter-badger/gitter-badge

Add a Gitter chat badge to README.md
renaming branch/tag tmp varible
Merge pull request #360 from bollwyvl/explore-branches

browser github branches
checks for ENV var GITHUB_API_URL so project works with GitHub Enterprise