Begin implementation of fromC marshaling functions for generated struct
types. This includes support for converting fields that are basic
primitive types such as string and integer types, nested anonymous
structs, nested libxl structs, and libxl built-in types.
This patch does not implement conversion of arrays or keyed unions.
Signed-off-by: Nick Rosbrook <rosbrookn@ainfosec.com> Reviewed-by: George Dunlap <george.dunlap@citrix.com>