Update JSON API documentation

Updates include:

    * We use constants as arguments in a overhead free way now, so
      integers are really integers and if one wants to specify stack
      positions, a special json object has to be used.

    * Removal of documentation sections saying something else.

    * Note that doubles are not yet supported.
Rewrote section about argument parsing
Merge pull request #271 from matthiasbeyer/fix-json_api_documentation

Update JSON API documentation