- Names ending with len sometimes referred to the buffer size.
The same names were used for both buffer size and string length
depending on the function in some cases.
- Rename str/string to path for generic path functions.
- Rename BLI_path_rel arguments (file, relfile) to (path, basename)
as it wasn't so clear which is being made relative, `file` can be a
directory so rename to `path` (matches naming for BLI_path_abs).
aa7d7c8e4b