Turns cell text into a theory file.
In :auto header mode the text is wrapped as
theory <theory> imports <imports> begin … end; in :manual mode the text
is a complete theory and its name is read from the header. All theories of a
runtime share one directory, so a cell can import another cell's theory.
Summary
Functions
Builds the theory for text. Options: :theory, :imports, :header_mode.
Writes the theory file.