v0.5.0

This release includes PR from #110 to #161. The highlights are:

• Wavefunction, currents, density plotting with VegaLite and other vlplot enhancements: #110, #111, #116, #126, #128, #138, #139, #140, #141, #152
• Unflatten to restore orbital structure in matrices, vectors, subspaces...: #112, #161, #147
• Can do algebra with Hamiltonians (sum, linear combinations...): #113
• Can do boolean combinations of RegionPresets: #129
• Fixes to unitcell: #117 (still needs some more)
• Much better handling of degeneracies in bandstructures, including topological defects as Dirac points: #124, #119, #125, #127, #145
• Dangling bond removal with mincoordination: #131, #133
• Remove invalidations for faster compilation: #132
• Indexing into bandstructure gives interpolated eigenpairs: #134
• Add Hexagonal Closed Packing lattice preset: #157
• Implement the deflated Schur algorithm for quasi1D Green functions: #161