g16.prep interface with xtb/turbomole

[polyluxus]

The script should be able to read an xyz coordinate file from a previous run of xtb. For example it should be able to extract a block with given charge/ uhf status in the following form:

$set
chrg <num>
uhf <int>
$end

Additionally it would be great if it recognises and parses coord files, as xtb -siman writes one for every conformer. Should be as simple as matching a line versus $coord, and having the format

   <floating point number>   <floating point number>   <floating point number>    <element>

where <floating point number> is in bohr. (Needs to be converted to angstrom, or can possibly be set with Units.)