v0.6.0

This is a full rewrite of Quantica.jl, see #198, and a breaking change. The highlights

• Syntax changes: unitcell -> supercell, bandstructure -> bands, parametric -> hamiltonian, transform(f, h) -> transform(h, f)... and possibly more.
• New features: Quite a few. Check the new manual (work in progress) and doctrings

Once this is tried and tested for a bit it will become v1.0