Boolean regions

[pablosanjose]

Closes #121

This introduces boolean operators &, I, xor and ! for RegionPresets.Regions

This also fixes a little bug in supercell that could lead to empty lattices when searching for sites did not immediately turn up a candidate.

It also introduces convenience aliases LP for LatticePresets, HP for HamiltonianPresets and RP for RegionPresets

Usage example

h = LatticePresets.honeycomb() |> hamiltonian(hopping(-1)) |> 
    unitcell(region = xor(RP.circle(10), RP.circle(6, (3,0)), RP.circle(6, (-3,0))))

[codecov-io]

Codecov Report

Merging #129 into master will increase coverage by 0.05%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #129      +/-   ##
==========================================
+ Coverage   59.98%   60.04%   +0.05%     
==========================================
  Files          16       16              
  Lines        2804     2808       +4     
==========================================
+ Hits         1682     1686       +4     
  Misses       1122     1122              

Impacted Files	Coverage Δ
src/Quantica.jl	100.00% <ø> (ø)
src/lattice.jl	81.81% <100.00%> (ø)
src/presets.jl	36.84% <100.00%> (+4.76%)	⬆️

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