Add messy_linelist() function

[joshwlambert]

This PR adds the messy_linelist() function to the package (closes #183). This function takes the output of sim_linelist() or the first list element of the output of sim_outbreak() and converts the clean line list data into messy line list data.

A new internal function, .spelling_mistake() is added which is called by messy_linelist().

Unit tests are added for the messy_linelist() function.

The {english} package is added as an Imported dependency in the DESCRIPTION. This is called by messy_linelist() when int_as_word = TRUE (which it is by default) to convert integers into words.

The README is updated to include:

• {cleanepi} in the Complimentary R packages section
• {messy} in the Related projects section

The design-principles.Rmd vignette is updated, adding a bullet point on the function naming convention for exported post-processing functions (renaming of truncation() required, #186), and adding {english} to the list of hard package dependencies.

[github-actions]

This pull request:

• Adds 1 new dependencies (direct and indirect)
• Adds 1 new system dependencies
• Removes 0 existing dependencies (direct and indirect)
• Removes 0 existing system dependencies

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