Set the stage to pack and push 31.0.0-pre1 CefSharp NuGet for #137

- Bump version series from 3.<something> to the new 31.0.0-pre1. Note with this we don't even have a clash with unofficial version id's pushed to staging.nuget.org :-)
- Change `cef.redist` dependency version indicator to allow auto-update or install of latest & greatest in the 3.1650.1562 series
Let's add a <licenseUrl> to packages
Cefsharp.Common.targets: cleanup and don't hijack AfterBuild
Update CONTRIBUTING.md

Separated document into sections, made some formatting changes, making text bold where required.
Added additional coding style guidelines
Added Section on PR's and Feature Branches
Update CONTRIBUTING.md

Added 132 columns
Update CONTRIBUTING.md

+ 'with' in the last bullet point 
Minor spelling nit
Merge pull request #323 from jornh/patch-1

CONTRIBUTING.md clarification
Split stuff which should have been on separate lines from the start
CONTRIBUTING.md - please no #Regions
Merge pull request #314 from jornh/prepare-to-pack-31.0.0-pre1

For #137: Set the stage to pack and push 31.0.0-pre1 CefSharp NuGets
@jornh, you missed this one. :)
Fixed copyright to indicate that we are now on the 2014 side of things.
...and also refer to just "the CefSharp Authors", since the CefSharp Project is not really a legal entity in its own.
Apparently, I missed some files in my earlier commits. Bummer!
There is no spoon, yet...
Let's upgrade this one while we're at it.
Update README.md

Undo one tiny bit of global search/replace