Add short Tutorial for contextual values
Fix various spelling errors

- allows to -> allows one to
- altough -> although
- begining -> beginning
- commiting -> committing
- dont -> don't
- hierachy -> hierarchy
- lets -> let's
- paramter -> parameter
- powerfull -> powerful
- recogniced -> recognised
- splitted -> split
- transfered -> transferred
- unkown -> unknown
Merge pull request #18 from pinotree/spelling-fixes

Fix various spelling errors
github infos + add NEWS
Merge upstream changes

Merge remote-tracking branch 'upstream/master'