Add LanHEP to conda-forge

[matthewfeickert]

https://theory.sinp.msu.ru/%7Esemenov/lanhep.html

Required by Micromegas (https://lapth.cnrs.fr/micromegas)

[matthewfeickert]

MicrOMEGAs v5.2.1 uses LanHEP v4.0.0 (2020-01-16) so that should be packaged first in the interest of Issue #86.