greatly simplify variable access/storage in transpiler

[openorclose]

this should fix #538 too

old

first run:

let a = 1;
{
 const b = 1; // not stored
}

transpile->

let a = 1;
{
 const b = 1; // not stored
}
globals.set("a", {getValue = () => a, setValue: v=> a = v});

second run:

a = 2;

transpile->

globals.get("a").setValue(1); // basically need to replace all references to `a` with this

after this refactor

we expose a evaller function that gets replaced each time to close around the values

(evaller is simply eval the first time a program is run)
first run:

let a = 1;
{
 const b = 1; // not stored
}

transpile->

evaller = nextProgram => eval(nextProgram);
let a = 1;
{
 const b = 1; // not stored
}

second run:

a = 2;

transpile->

evaller = nextProgram => eval(nextProgram);
a = 2;

note that on the second run, this program is run in the scope of the previous program using the replaced evaller, so no complicated code is needed to transform top level vars into object accesses.

[coveralls]

Pull Request Test Coverage Report for Build 934160766

• 41 of 42 (97.62%) changed or added relevant lines in 5 files are covered.
• 2 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.07%) to 83.728%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/transpiler/transpiler.ts	29	30	96.67%

Files with Coverage Reduction	New Missed Lines	%
src/transpiler/transpiler.ts	1	92.13%
src/utils/astCreator.ts	1	84.09%

Totals
Change from base Build 932954521:	-0.07%
Covered Lines:	7331
Relevant Lines:	8472

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💛 - Coveralls

[thomastanck]

LGTM, theory checks out, tests pass, and coverage is good. Did a tiny bit of manual testing as well.