GitLab

Correct documentation so all commands should be run from the root
of the git directory.

Also clarifies usage on label maps. In a nutshell, label map IDs
should start at index 1 (and not include 0).

* Change dictionnaries iteritems() to items()

Also use the url link to github because *.md files are not
rendered when using jupyter notebook

1 should not shuffle during evaluation; 2 num_readers should be one, or each sample would be evaluate for (num_reader) times and only (num_examples / num_reader) distinct samples are evaluted.

dictionary having both 'tuple' and 'str' keys cannot be 'sorted'

iteritems() -> items()

* make batcher compatible for py3

* make prefetcher and operations in ops compatible for py3

* use six.iteritem

* make all tests in  compatible with py3

* simplify usage of six and modify import order

* add back the space line

This works around a bug in earlier proto versions
that automatically infer these values to be integer
instead of float.