write xyz format file for PDB-CCD

PDBeChem currently provides xyz format files

https://en.wikipedia.org/wiki/XYZ_file_format

not sure how useful they are is but easy to write so just implement.

current files:

• ideal coordinates

cat /nfs/ftp/pub/databases/msd/pdbechem/files/xyz/EOH.xyz 
9
EOH
C    0.0070   -0.5690    0.0000
C   -1.2850    0.2500   -0.0000
O    1.1300    0.3150   -0.0000
H    0.0390   -1.1970    0.8900
H    0.0390   -1.1970   -0.8900
H   -1.3170    0.8780    0.8900
H   -1.3170    0.8780   -0.8900
H   -2.1420   -0.4240    0.0000
H    1.9860   -0.1370    0.0000

• model coordinates:

cat /nfs/ftp/pub/databases/msd/pdbechem/files/xyz_r/EOH.xyz 
9
EOH
C   15.2120   49.1980    7.4910
C   16.0690   50.3860    7.1040
O   15.8610   48.1850    8.2560
H   14.3750   49.5790    8.0940
H   14.8580   48.7310    6.5600
H   15.4670   51.0980    6.5200
H   16.4420   50.8800    8.0130
H   16.9200   50.0420    6.4980
H   15.2440   47.4880    8.4470

• Currently elements are upper case:

cat /nfs/ftp/pub/databases/msd/pdbechem/files/xyz/FES.xyz                                                                                                                                   
4
FES
FE   0.0000   -0.2130   -1.5310
FE   0.0000   -0.2130    1.5310
S    1.4610    0.3720    0.0000
S   -1.4610    0.3720    0.0000

but better if the iron atoms are written as Fe.