Creates a CommandDocumentation given command string, arg parser, and a CommandDocumentationContent.

ParseArgsOrDie is used for CLI command that should exit after erroring.

CommandDocumentation is a struct that represents all the data structures required to create the documentation for a command.

This type is to store the content of a documented command, elsewhere we can transform this struct into other structs that are used to generate documentation at the command line and in markdown files.