Small patch converts the MolFormManip to use StringBuilder and only output subscript when > 1. The the toString() already did this but the HTML for methane would be 'C1H4' it is now 'CH4'.
Last two commits: https://github.com/johnmay/cdk/commits/fix/html-formula
Miguel, please let me know if this was not OK.
It is perfect. I think it is much more clear for the user presenting CH4 instead of C1H4.