Simplify return values (#114)

Introduce bk_err and bk_bool rather than using int for both of these.
This means that the function definition now specifies whether 0 means
no error, or whether it means false.

compile_headers.py

@@ -50,7 +50,11 @@
 for filename in sorted(glob.glob(os.path.join(folder_path, '*.h'))):
     with open(filename, 'r') as file:
         text = file.read()
-        header += text.split("*/", 1)[1]
+        entire_file = text.split("*/", 1)[1]
+        split_around_include = entire_file.split('#include "all.h"\n\n', 1)
+        header += split_around_include[0]
+        if len(split_around_include) == 2:
+            header += split_around_include[1]
 
 containers_header_file = open("containers.h", "w+")
 containers_header_file.write(header)