More robust bond sanity check

[eahenle]

Existing bond sanity check looks at 3 things:

• Are there zero-valent atoms?
• Are there multivalent hydrogens?
• Are there hypervalent carbons?

Good start, but I think we can do better. First, not all structures need all of these checks; e.g. COFs may be halide salts, or some structures may include hydrogen-bonded moieties. It would be good to be able to flag off any individual check. Second, there are other possible checks that could be made, such as minimum/maximum valency for various atoms.

Idea: dictionary of sanity check rules. rules::Dict{Symbol, Union{Vector{Int},UnitRange{Int}}) So, e.g., :H => [1], :C => 1:4
Then the bond_sanity_check signature could be: bond_sanity_check(crystal::Crystal; rules=rc[:bond_sanity], add_rules=Dict())

If the user wants to provide a complete set of rules, they use the rules kwarg. If the user wants to just modify some rules without changing the global set, they use add_rules. The sanity check is performed using rules = merge(rules, add_rules)

[eahenle]

Could also take some inspiration from the ARC-MOF bond checks