v0.6.0

Breaking change: The simulation box is now an optional property of the system.
- This change affects the return type of various functions that access the simulation box.
- High-level methods of the System structure now return errors if they require a simulation box and it is not present.

Breaking change: Higher-level System and Atom methods no longer panic when encountering an atom with an undefined position; instead, they return a recoverable error.

Added the Elements structure, which defines properties of supported elements.
The Elements structure can be constructed from a YAML file containing element definitions by calling Elements::from_file.
Default properties of the elements supported by groan_rs are stored in src/config/elements.yaml. A default Elements structure, containing elements and their properties from this YAML file, can be constructed using Elements::default.
The Elements structure can be updated using Elements::update. In this case, another Elements structure must be provided, specifying the changes to be made to the original Elements structure.
Elements can be guessed for the atoms of the system using System::guess_elements.
Bonds can now be guessed for the system using System::guess_bonds. This requires van der Waals radii to be assigned to individual atoms. Van der Waals radii can be guessed based on the elements.

Breaking change: The macro @hydrogen is no longer supported. Use element name hydrogen instead.
Bug fix: Invalid queries containing a command in parentheses followed by anything other than a binary operator (e.g., (name CA CB) resname LYS) no longer cause a panic but instead return a proper error.
Atoms can now be selected based on their element name or element symbol (element name carbon or element symbol C). This requires atoms to have assigned elements.
Atoms that are part of the same molecule can now be selected using the molecule with operator. For example, molecule with serial 13 will select all atoms that are part of the same molecule as the atom with number 13. This requires the system to have topology information.

Introduced System::group_get_com for calculating the center of mass of a group of atoms using the Bai and Breen algorithm. Note that all atoms in the target group must have mass information.
Introduced System::atoms_center_mass as an alternative to System::atoms_center but using center of mass instead of center of geometry.

Breaking change: The System::set_mol_references method is no longer public.
Added more tests for the basic Atom get_*, set_*, reset_*, and with_* functions.
Documentation examples no longer repeat that you have to use groan_rs::prelude::*.
Added Atom::distance_naive for calculating the distance between atoms without considering periodic boundary conditions.
Bug fix: Vector3D::wrap_coordinate and Vector3D::min_image now panic if box_len is 0 instead of looping indefinitely.
The System::group_get_center function has been refactored and may return a result that is not binary identical to previous versions.
Introduced System::group_isempty function for checking whether a target group of atoms is empty.

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