Clean 3-working-with-git index
Describe of "fork a repo" operation
Describe "clone remote repo" operation
Describe "configure remotes" operations
Minor fix in "clone remote repo" operation
Describe "fetch remotes" operation
Describe "create a new branch" operation
Describe "commit-changes" operation

It also include some placeholders for "The Index" concept and "Commit conventions"
Add place holders for some operations

* push-to-a-remote repo
* creating-a-pull-request
* working-with-pull-requests
* merge-remote-branches
Add staging area concept
Merge remote-tracking branch 'origin/gh-pages' into git-operations
Minor fix on http://gitref.org/basic reference
Fix fork-a-repo-fork-button.png image
Add clone and fork concepts
Merge pull request #7 from matiasbeckerle/git-concepts

Starting git concepts
Merge remote-tracking branch 'origin/gh-pages' into git-operations

Conflicts:
	2-concepts/index.md
Fix scenario word in configure-remotes
Add internal behavior of Git

* Also updated References.
Fix glossary words styles
Add objects explanation

* Tree objects.
* Commit objects.