The complexity of the create() routine justifies the move to another file.
This commit implements the create() functionality which creates a TOML
tempfile which the user should edit and then reads the contents to build
the Vcard object which then gets written to either stdout or the
destination file.
Besides that:
* Move helper function to util module
* Rewrite and fix tests
* Implement contact listing with formatting via commandline or config
* Implement importer functionality for contact
* Implement "show" subcommand
* imagrc.toml: Add explanation which fns are supported in templates
