Style preservation in AST

[LPGhatguy]

We probably want to hold off on jamming style information into the AST until we have complete grammar coverage.

How can this be done in a way that isn't too cumbersome?

A sample block, with all the places we care about whitespace being marked:

<HERE>if <expression><HERE>then
    <chunk>
<HERE>elseif <expression><HERE> then
    <chunk>
<HERE>else
    <chunk>
<HERE>end

Since we always consume whitespace before a token, any whitespace before <expression> or <chunk> belongs to those AST nodes instead, which simplifies things a bit.