* capture->stdout.len the number of bytes read. capture->stdout.buf
* is null terminated, so as long as the child's output is textual,
* you can use it as a string. Similarly, child's stderr is in
- * capture->stderr.buf and capture->stderr.len.
+ * capture->stderr.buf and capture->stderr.len. Caller is responsible
+ * for freeing the result with free_capture().
capture_child(const char *file, char *const argv);