Just strings and numbers for now

I think there’s a better way to do type checking so I’m going to hold off on it for now and get basic functionality working for now and come back later.

This class exposes two functions. `evalNode` take an AST node and evaluates it down to simplest terms. `eval` takes an array of AST nodes and calls evalNode on each of them. I don’t think we’re quite ready to be producing HTML yet so let’s not get ahead of ourselves.

Currently I'm relying on JavaScript's semantics
around truthiness. I think I'm going to retain
that ease of use (i.e. `(if list #t #f)` should
return true if the list has more than 0 elements,
etc) but I want to specify that behavior myself.

Just numbers and strings for now

It's a little hacky and not very clean but it's
working for now.

What was happening was that spaces were allowed in
all literals to account for quoted strings, but
this meant that two identifiers in a row would get
parsed as a single literal. This commit sets a
flag to allow whitespace in literals when a quote
is encountered and then unsets that flag at the
next quote.

No variables or conditionals or anything yet, just
the basic ability to turn s-expressions into HTML.