Horizontal bar graph prints legens keys with --keys

If you use --keys in conjunction with horizontal bar graphs, the data points
will be read as key-value pairs. Valid delimiters are space characters, colons
or equals sign.
Make the axis graph accept (and drop) legend keys
We now use value-key pairs, in stead of key-value

If --keys/-k is specified on the command line, all the data that follows after
the first space is used as legend keys. If --keys/-k is omitted, the data is
silently ignored.
Bugfix in extents calculation
Updated the help
Version 0.2.21.1 (testing version, will not be released as this version)