[REFACTOR] Evaluate if we can remove the man folder from the repository

[tbouffard]

See #26 (comment)

The man folder contains only generated files except bpmnVisualization-package.Rd
This file could be generated as done in https://github.com/bergant/bpmn/blob/9768cccc551831846a6d404271e330d710c8ef3b/R/bpmn.R#L1 (add roxygen comments on a NULL statement)

We will probably use Roxygen2 that generates the Rmd files from documentation as R comments located in the source code (see https://kbroman.org/pkg_primer/pages/docs.html and https://r-pkgs.org/man.html)
Once roxygen2 is installed, documentation can be generated by calling devtools::document()
See also https://github.com/r-lib/roxygen2

The NAMESPACE file is also generated

To avoid roxygen2 warning roxygen2 requires Encoding: UTF-8
Add Encoding: UTF-8 to the DESCRIPTION file --> done in #49

For contributors, document RStudio configuration to be setup to avoid running doc generation when changing the code
The following in the default configuration. Some files aren't generated if the config is left unchanged.