Update README.mdown

Add brief description of major API changes.
Updated SQLiteApiWP8 to use sqlite-net-wp8
Merge pull request #2 from ncipollina/master

Updated SQLiteApiWP8 to use sqlite-net-wp8
Unify the WP8 platform projects (remove csharp-based sqlite platform version, use sqlite-net-wp8 nuget-based platform project instead)
Add nuget spec etc for WindowsPhone8 platform project/nuget
Modify async code to improve task/scheduler default behavior.

Pass TaskCreationOptions.DenyChildAttach to tasks by default.
Ensure TaskScheduler.Default is evaluated when the task is created (instead of in constructor)