Added pre-fetching of entire dataset into memory where possible.
Removed defunct nearest neighbours code from lattice constructor
Added C++ code for anisotropic lattice
Tiny formatting alteration in lattice constructor.
Added anisotropic tadpole coefficients to Lattice C++ class
Removed pickling capability from lattice.
Fixed propagator init example to follow new function arguments.
Exposed anisotropic lattice options to python.