[devlead]

• Sanitize generated class names from assembly names with characters that are invalid in identifiers, e.g. Cake.Markdown-Pdf.
• Emit generic constraints on alias wrappers, including unmanaged, notnull, class?, nullable constraint types and allows ref struct.
• Emit enum defaults as member names or flags combinations, falling back to a cast.
• Fix decimal, float and double literals, NaN and Infinity, and default for value types and type parameters.
• Skip aliases whose signature references unresolved types and report CAKEGEN001.
• Skip CakeNamespaceImport values that are not namespaces and report CAKEGEN002.
• Read CakeNamespaceImport from the declaring class and assembly as well as the method.
• Escape C# keyword identifiers in method, parameter, type parameter and property alias names.
• Keep ref readonly parameters and forward them with in.
• Add addin compatibility tests using in-memory fake addins, and reference the full shared framework in test compilations.

fixes #253