read_buffer() - read from a file and return a buffer, or return part of
a buffer as a string
string | buffer read_buffer( string | buffer src,
int start, int len );
If 'src' is a string (filename), then the filename will be read, start‐
ing at byte # 'start', for 'len' bytes, and returned as a buffer. If
neither argument is given, the entire file is read.
If 'src' is a buffer, then characters are read from the buffer begin‐
ning at byte # 'start' in the buffer, and for 'len' # of bytes, and
returned as a string.
Note that the maximum number of bytes you can read from a file and into
a buffer is controlled via the 'maximum byte transfer' parameter in the
runtime config file.
write_buffer(3), allocate_buffer(3), bufferp(3), read_bytes(3),