Update src/Portable.Licensing/Validation/LicenseValidationExtensions.cs
Add icons
Rename .txt file to .md
Update project url
Update FAKE to 2.1.145
Add Xamarin's package manager tool
track renaming of the license file
Add a Getting started document
Merge remote-tracking branch 'sven-s/patch-2' into devel

Fixed issue #133
Added xpkg packaging build target

fixes #132