Very basic slab creation code.
Finetune slab generation.
Add shift.
iMinor refactoring.
Minor fix to tolerance.
IMprove doc and unittest.
REmove use mirrors for travis.
Reduce miller indices for greater efficiency in slab generation.
Minor refactoring of slab generation code.
Use pre-computed recp lattice for calculating the crystallographic reciprocal
lattice.
Update spglib to dev version (on github). Fixes #93.
Merge branch 'surface'