Check the arguments passed to ./configure.

For now, don't allow arguments, since ./configure doesn't actually
support any.  Previously "./configure --help" would print misleading
information, and any other arguments were silently ignored.

Thanks to Alexander Barton <alex@barton.de> for the report.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Reviewed-by: Zoran Zaric <zz@zoranzaric.de>
Explain current installation process in README.md (i.e. "make install").

Signed-off-by: Rob Browning <rlb@defaultvalue.org>