Add contribution guidelines

I've added a _Contributing_ section to the README and a [CONTRIBUTING
file](https://github.com/blog/1184-contributing-guidelines). I do not
expected for these changes to be merged right away, as they can be seen
as a draft from what I've observed in the past weeks. The intention here
is not only help the developers that are new to the project, but also
make it easier for Anders to deal with new patches.
Add a note about notification on pull requests
Add a note about rebasing pull requests
Merge pull request #68 from myhro/new-contributing

Add contribution guidelines
Fix some typos on the CONTRIBUTING file
Add info about gh-pages-dev on CONTRIBUTING
Add missing unstable configuration fixing EC2 image building problems.
Merge pull request #77 from rybaktomasz/fix-upstream

Add missing unstable configuration fixing EC2 image building problems.
Fix SetMetadataSource predecessors

Added GenerateLocale as SetMetadataSource predecessor, to avoid any
potential locale warnings. Also fixed a space indentation flaw and a
string which was being formatted with a non-existent key-argument.

This closes #75.
Add Travis CI

By now, it will only test the coding style rules defined for the
project, which are basically a few exceptions to the PEP8.
PEP8 fixes
Add information about coding style checking

Added a note about this to the CONTRIBUTING.md file. [skip ci]
Expose debootstrap include/exclude in manifest.
This is useful in many cases in which the next steps of bootstrapping the image depends on the packages, for e.g to use a non-conventional repository transports like https.
Be pythonic.
Use sets.update method to add pacakge names.
Add salt plugin
 - uses salt bootstrap to install minion code
 - custom grains can be set.
 - option to specify master in the manifest.

e.g manifest (TODO: Add this to doc.)

"salt": {
            "install_source": "git",
            "version": "develop", \\ Only if the source is git
            "master": "", \\ salt master ip or fqdn
            "grains": {
                "custom_grain1": "custom_grain_value1",
                "custom_grain2": "custom_grain_value2",
            }
        }
Merge pull request #82 from dbalan/expose_debootstrap_include

Expose debootstrap include/exclude in manifest.
Merge pull request #84 from dbalan/saltstack_minion

Add salt plugin.
Don't allow target in include/exclude_packages
Fix indentation in schema
Add changes by Dhananjay to changelog
Fix fetching of packages.components
Add update from master