#93 Support KCF file input

KCF is KEGG Chemical Format, and is a 2D molecular graph format similar to XYZ.

Example, the KCF for phosphate is (taken from http://kegg.jp/dbget-bin/www_bget?C00009+-kcf ):

ATOM 5
1 P1b P 27.1282 -21.2572
2 O1c O 25.9971 -21.9011
3 O1c O 28.4489 -21.8360
4 O1c O 27.4637 -22.7728
5 O1c O 27.1282 -19.9529
BOND 4
1 1 2 1
2 1 3 1
3 1 4 1
4 1 5 2