added examples for other nuclear data libraries, changed all to 300 K

The models currently in `/examples` use the ACE-format labels corresponding to the MCNP data libraries.  This PR adds inputs that use the Serpent, JEFF, and NNDC labeling schemes.  Also, all models - if they were not before - have now been set to a 300 K temperature to maintain consistency with the NNDC data which is only provided at 300 K.