Fix wren, improve logo implementation

logo: merge eval and eval-ast, fix defmacro, improve efficiency

Complete the merge of eval and eval-ast.

Prevent defmacro! from mutating functions.

Improve the performance:
* use native iteration in env_get and env_map
* rewrite the reader so that it does not create lots of
  substsrings of its input
* reduce the cost of most list operations
The previous implementation was using lots of temporary list
constructions (for example, reverse iteration with butlast requires
O(n^2) nodes). This commit does not require Dockerfile to change the
garbage collection settings anymore.

Encapsulate all representation in types.lg and env.lg.
Replace some manual iterations with logo control structures.
Reduce the diff between steps.

IMPLS.yml

@@ -1,2 +1,4 @@
 IMPL:
+#   - {IMPL: logo, NO_SELF_HOST: 1}  # step4 timeout
+  - {IMPL: logo}
   - {IMPL: wren}