Compile without unnecessary parentheses

[andreas-web]

This pull request adds functionality to JessieCode that compiles an AST without unnecessary parentheses.

To achieve this, the following changes are made:

• New function jc.minParentheses
• New command 'minParentheses' in jc._genericParse
• New parameter jcMinParens in the jc.compile function; its default value is false. This does not change anything in existing calls!
• In jc.compile:
  • Add parenthesis-avoidance functionality
  • Recursive sub-function compile. jc.compile is no longer recursive itself. This eliminates the need to always "pass on" the parameters js and jcMinParens

Additionally:

• _genericParse now receives its attributes as an object (for future compatibility)
• Some documentation improvements
• Some JessieCode tests

No changes have been made to the existing functionality. The new functionality is only used when calling board.jc.minParentheses or board.jc.compile(..., ..., true).