Update rubber plan

* Add brief definitions of each basic object the language
* Remove imprecise "Lexemes" sections from the definitions of an object
* Add >< (negation) to boolean and change ? (if) syntax
* Give more appropriate names to some components
  * Array instead of List (since it's unresizable)
  * Table instead of Generic object
  * Context instead of Symbol table
* Make table union return self
* Remove External object for now
* Update syntax of the Array literal
* Update syntax and semantics of Table literal
  * Table now can self-reference (@)
* More goals
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