Merge pull request #4 from blink1073/master

Pep8 fixes.
Update active contours
update readme
update readme
Update Readme.
update readme.
updated readme.
update readme
update readme
Merge pull request #5 from blink1073/master

Add helper files to convert matlab tours to Ipython notebooks.
added gradient computation
Merge branch 'master' of https://github.com/gpeyre/numerical-tours

* 'master' of https://github.com/gpeyre/numerical-tours:
  added gradient computation
  update readme
  update readme
  updated readme.
  update readme.
  Update Readme.
  update readme
  update readme
  Update active contours