OpSum, TOML

[Last-Hope-024]

This pull request introduces the following changes:

1. Renamed bonds.jl to opsum.jl

   • Users can now define operators using Op and collect them all in an OpSum.

2. Modified and tested the functions neighbor_bonds! and lattice_bonds

   • Both functions now work and return an OpSum().

3. Added write_OpSum_to_toml! functionality

   • Introduced an optional index_zero argument to enable zero-based indexing for site indices when writing to a TOML file.

4. Created an examples folder with two scripts

   • One for the triangular lattice and another for the Shastry-Sutherland lattice.

5. Added inline comments and documentation

[Last-Hope-024]

Included function to plots the interactions bonds in OpSum()

[awietek]

Thank you Rafael, this looks great. I would have one comment about naming conventions. I would like to stick to CamelCase for classes, e.g. OpSum, and snake_case for functions. Thus, I would like to ask you to rename:

plotOpSum -> plot_opsum
write_OpSum_to_toml -> write_opsum_to_toml
plotops -> plot_ops

Also, I would like to ask you to add a "docstring" explaining the functions and parameters. I think it would be great if this showed up in the documentation.

Anyway, great work.