Markdown test of variables substitution ('vars' command) with:
    - creation of vars. dictionaries
    - creation of vars.
    - substitution:
        - simple
        - with global vars.
        - with redefinition of var
        - to itself (see '*:*')
        - with usage of dictionary (see '*:$d1')
        - with value from dictionary (see '${d1.v1}'
        - overrding of global var. value
