Change some custom nodes to be regular AstNodes

[jdpage]

In particular, the entire jeff65.gold.storage module is gone, along with
jeff65.gold.passes.asm.AsmRun. As an additional advantage, some compiler
passes which were previously imperative are now pattern-based.

(This was rescued from PR #37 asm-blocks, where it was mixed in with a
bunch of other changes.)

[coveralls]

Pull Request Test Coverage Report for Build 273

• 10 of 14 (71.43%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.2%) to 89.464%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
jeff65/gold/passes/lower.py	0	2	0.0%
jeff65/gold/passes/resolve.py	0	2	0.0%

Totals
Change from base Build 270:	-0.2%
Covered Lines:	1490
Relevant Lines:	1657

---

💛 - Coveralls

[jdpage]

I feel slightly guilty about the slight reduction in test coverage, but it's honestly due to the fact that I deleted some code that was covered, and the four relevant uncovered lines are related to lowering, which is probably about to get rewritten as I pull things into backends. SO I'M LETTING IT STAND