CreateGenRequest creates a codegen request from a `FileDescriptorSet`.

FilesToGenerate iterates through the proto files in the request and returns only the ones that were requested on the command line.

FindDescriptor finds the named descriptor in the given set.

InStringSlice returns whether or not the supplied value is in the slice.

LoadDescriptor loads file descriptor protos from a file on disk, and returns the named proto descriptor.

LoadDescriptorSet loads a `FileDescriptorSet` from a file on disk.