added the amber2lt.py conversion tool
The newly added amber2lt.py program converts force-field files used by and created by AmberTools (such as FRCMOD and DAT files) into moltemplate (LT) format. The "gaff.lt" and "gaff2.lt" files were created with this program. Now users can use this tool as well with their own custom FRCMOD files.
The amber2lt.py script replaces amberparm_.py files and amber.sh scripts that were used before. (Those scripts were buggy and undocumented.)