Add new environments and improve commands.
Start the chapter on parsing.

  -- searching for text
  -- regular expressions
Work on the exposition of Dijkstra's algorithm.
Add global keyword to zelinar functions.
Bugfix: delete -> del.
Make code more readable.
Reformulace.
Kod k vyhledavani v textu.
Obrazky k vyhledavani v textu.
Kleene.
Interpret Turingových strojů.
Unify numbering of floats and environs + use unnumbered subsections in sec 4.
Remove unused environments.
Mention the Boyer-Moore algorithm.
Make subsections unnumbered.
Fix environments.