libdrgn: python: rename module.c to main.c

We're eventually going to add a drgn.Module class, which logically
should go in a file called module.c. But, we already have a module.c
with module-level definitions. Rename that file to main.c to free up
module.c

Signed-off-by: Omar Sandoval <osandov@osandov.com>

libdrgn/Makefile.am

@@ -147,7 +147,7 @@ _drgn_la_SOURCES = python/constants.c \
 		   python/error.c \
 		   python/helpers.c \
 		   python/language.c \
-		   python/module.c \
+		   python/main.c \
 		   python/object.c \
 		   python/platform.c \
 		   python/program.c \