lang: Split lang package out into many subpackages

This is a giant refactor to split the giant lang package into many
subpackages. The most difficult piece was figuring out how to extract
the extra ast structs into their own package, because they needed to
call two functions which also needed to import the ast.

The solution was to separate out those functions into their own
packages, and to pass them into the ast at the root when they're needed,
and to let the relevant ast portions call a handle.

This isn't terribly ugly because we already had a giant data struct
woven through the ast.

The bad part is rebasing any WIP work on top of this.

lang/Makefile

@@ -20,23 +20,23 @@ SHELL = /usr/bin/env bash
 
 all: build
 
-build: lexer.nn.go y.go interpolate/parse.generated.go
+build: parser/lexer.nn.go parser/y.go interpolate/parse.generated.go
 	@# recursively run make in child dir named types
 	@$(MAKE) --quiet -C types
 
 clean:
 	$(MAKE) --quiet -C types clean
-	@rm -f lexer.nn.go y.go y.output interpolate/parse.generated.go || true
+	@rm -f parser/lexer.nn.go parser/y.go parser/y.output interpolate/parse.generated.go || true
 
-lexer.nn.go: lexer.nex
+parser/lexer.nn.go: parser/lexer.nex
 	@echo "Generating: lexer..."
-	nex -e lexer.nex
-	@ROOT="$$( cd "$$( dirname "$${BASH_SOURCE[0]}" )" && cd .. && pwd )" && $$ROOT/misc/header.sh 'lexer.nn.go'
+	nex -e -o $@ $<
+	@ROOT="$$( cd "$$( dirname "$${BASH_SOURCE[0]}" )" && cd .. && pwd )" && $$ROOT/misc/header.sh 'parser/lexer.nn.go'
 
-y.go: parser.y
+parser/y.go: parser/parser.y
 	@echo "Generating: parser..."
-	goyacc parser.y
-	@ROOT="$$( cd "$$( dirname "$${BASH_SOURCE[0]}" )" && cd .. && pwd )" && $$ROOT/misc/header.sh 'y.go'
+	goyacc -v parser/y.output -o $@ $<
+	@ROOT="$$( cd "$$( dirname "$${BASH_SOURCE[0]}" )" && cd .. && pwd )" && $$ROOT/misc/header.sh 'parser/y.go'
 
 interpolate/parse.generated.go: interpolate/parse.rl
 	@echo "Generating: interpolation..."