Added documentation

  - doc/ZSpec11.txt is the Z-Machine Standard 1.1 Document
  - doc/czech is the Comprehensive Z-machine Emulation CHecker
  - doc/frotz is a Z-machine implementation complying to the 1.0
    Standard.

  see also:
  - http://www.ifarchive.org/indexes/if-archiveXinfocomXinterpretersXspecification.html
  - http://www.ifarchive.org/indexes/if-archiveXinfocomXinterpretersXtools.html
  - http://frotz.sourceforge.net/