[Diff since v2.7.3](v2.7.3...v2.7.4)

- Fix printing of one-letter codes for custom residues that do not have three-letter code names, but were defined in PDBTools (ex: SIRAH force-field residues).
 - Run CI on 'pre'.
 - Fix doc typos.

[Diff since v2.7.2](v2.7.2...v2.7.3)

- fix call to mean and std in write function ("Statistics not defined error").

update docs

improve warning doc message

[Diff since v2.7.1](v2.7.1...v2.7.2)

- fix doc typo
- fix conversion factor in header section of human-readable output
- update references with new article of V. Piccoli.

[Diff since v2.7.0](v2.7.0...v2.7.1)

- better support for non-standard residue names in `ResidueContributions`.

[Diff since v2.6.2](v2.6.2...v2.7.0)

- The `ResidueContributions` object can be sliced and indexed, to obtain the contributions of subsets of the structures, returning `ResidueContributions` objects.
- The `ResidueContributions` object can be multiplied and divided by scalars, to possibly renormalize the values.
- The computation of `ResidueContributions` is parallel and displays a progress bar, which can be disabled with the `silent` option.

- `contourf(::ResidueContributions)` does not fail for residue-names with other than 3 letters.

[Diff since v2.6.1](v2.6.1...v2.6.2)

- Fix automatic setting of `colorscale` when `clims` is manually defined.

[Diff since v2.6.0](v2.6.0...v2.6.1)

- Remove dependency on StyledStrings, which caused a REPL temporary halt after `using ComplexMixtures`.

[Diff since v2.5.1](v2.5.1...v2.6.0)

- `contourf` support all standard `Plots.contourf` keyword arguments.
- better automatic color and levels choices for `contourf`
- `ResidueContributions` is shown with :bwr colorscale if values range around zero.