fix trailing whitespace
a step towards uniform code directives
fixup the way exercise arrays are displayed
better use of lists and syntax
scale the numpy indexing picture a bit better
be explicit about code-blocks
better scaling of second indexing diagram
strip traling whitespace
uniform code-blocks in the numpy operations section
syntax
remove trailing whitespace
uniform prompts

The more advanced stuff was not changed, since it is repeated in the advanced
numpy section and will be deleted from this section soon.
prompt fixes etc..
move duplicate content from intro numpy to advanced numpy
intro/numpy/elaborate_arrays.rst: fix failing doctests, apparently trailing whitespace is needed
bring back in the intersphinx mappings

Somehow the intesphinx mapping for numpy is bust.
README.rst: mention the intersphinx directives
migrate section Editorial Policy into the guide
move section on using markup
move section on using github to contribute