nslice/__init__.py: added method "hkl"
nslice.xtalori: minor (show a use of nslice.hkl)
moved neutron related basic stuff into nslice.neutron
added nslice.mc to work with Monte Carlo related work
nslice.spe2hkle: fixed import of neutron unit conversion module
added command "sxr"
README.md: added dependency on docopt