Improve tools/obconformer.cpp

[e-kwsm]

• Enable to accept forcefield (default: MMFF94)
• remove unused variables
• clang-format

[e-kwsm]

At present it is impossible to change the forcefield from MMFF94, so we cannot perform obconformer on some systems, e.g., borane.

In this PR I simply add forcefield as the last argument—use it if passed, otherwise defaulted to MMFF94.

[ghutchis]

I don't use this tool directly, or i would have noticed the issue. Adding an option is a good choice, but the default should be:

• use MMFF94 if possible
• if not, use UFF

if the user actually asks for a specific forcefield, then try it or fail

If you're willing to make that small change, i'll happily accept the patch, thanks.

[e-kwsm]

Adding an option is a good choice, but the default should be:

• use MMFF94 if possible
• if not, use UFF

if the user actually asks for a specific forcefield, then try it or fail

Implemented.

[ghutchis]

Thanks - definitely improved 😄