Rename the iio documentation files to ReST, add an
index for them and adjust in order to produce a nice html
output via the Sphinx build system.

The cdrom.txt and hdio.txt have their own particular syntax.
In order to speedup the conversion, I used a small ancillary
perl script:

	my $d;
	$d .= $_ while(<>);
	$d =~ s/(\nCDROM\S+)\s+(\w[^\n]*)/$1\n\t$2\n/g;
	$d =~ s/(\nHDIO\S+)\s+(\w[^\n]*)/$1\n\t$2\n/g;
	$d =~ s/(\n\s*usage:)[\s\n]*(\w[^\n]*)/$1:\n\n\t  $2\n/g;
	$d =~ s/(\n\s*)(E\w+[\s\n]*\w[^\n]*)/$1- $2/g;
	$d =~ s/(\n\s*)(inputs|outputs|notes):\s*(\w[^\n]*)/$1$2:\n\t\t$3\n/g;
	print $d;

It basically add blank lines on a few interesting places. The
script is not perfect: still several things require manual work,
but it saved quite some time doing some obvious stuff.

At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>