Add simple example

that shows how to:
* load from/save to file
* access data and affine
* some other simple functionalities

Remove unnecessary space
Merge pull request #324 from lesteve/add-simple-example

Add example to show simple nilearn functionality
Break down plot_demo_plotting.py in two smaller examples

plot_demo_more_plotting.py contains the most advanced usages of plotting
Fix broken links related to plotting documentation
Merge pull request #327 from lesteve/break-down-plotting-examples

Break down plotting example
DOC: use link rather than manually updated list of functions
DOC: missing dot in README.rst
DOC: remove stray 'n'
reorder_img was modifying the input image affine

fixes #325
added auto_resample to concat_niimgs()
cleaned concat_niimgs test
cosmetics + regexp call now internal
fix merge conflict