Updated version to alpha release
Implemented CEP attribute
Updated NuGet spec file: version, tags and frameworks
Marked all the attributed as sealed. This change fixes #3.

Marked all the attributes as sealed in order to avoid search in attribute inheritance hierarchy and unintended code execution.

For more information about sealed attributes, see http://msdn.microsoft.com/en-us/library/ms182267.aspx
Updated release notes in the NuGet spec file.
Configured project to generate documentation.