Adding Fluka Usrbin

Modelled on mcnp Meshtal and Meshtally. Adds support for Fluka usrbin (mesh tallies).
Yes. This was the file that was used to make the usrbin test files. I wasn't sure if it should be included or not but the mcnp test input files were included so I submitted this as well. I will see if comments can be added and do that.