/**             
 * @brief reads a file into a given buffer
 * @param[out] buffer The memory area where the file contents are written to.
 * @note buffer is not null terminated at the end of file reading
 * @param[in] len The length of the supplied memory area.
 * @param[in] f The file which is to be read into the memory area.
 *
 * @note Properly handles partial reads
 */