start adding syntax tree nodes
include ast nodes in parser
find numbers and variables
some binary operations
order of operations
add assign statement
introduce parentheses
dump parse tree in dot format
implement statement list grammar productions
define input as start token

Allows for successful parse of empty file and easy change when functions are introduced.
type system
top level variable declaration
top level variable initialization

Currently only constants are valid assignment values.

This may change in the future, time permitting.
grammar for external declaration list
use external declarations as foundation for program

Statement list was a placeholder.
grammar for function declarations
add optional parameter list to functions
add return to parsing