Fix use of macroexpand-all in loopy-iter and loopy.

We should always be passing an environment to the function, otherwise the
environment is reset to nil, which breaks macros like `cl-flet`.

- Stop doing top-level and sub-level expansion with different functions.
  - Instead, add `loopy-iter--level`.
  - Remove `loopy-iter--sub-level-expanders`, `loopy-iter--top-level-expanders`,
    `loopy-iter--macroexpand-sub`, `loopy-iter--macroexpand-top`,
    `loopy-iter--keyword-expander-sub`, and `loopy-iter--keyword-expander-top`.
- Pass the macro temporary environment in all places where we didn't before:
  - `loopy-iter`
  - `loopy`
  - `loopy-iter--parse-at-command`
  - `loopy-iter--opt-accum-expand-val`
- Add a `loopy--with-protected-stack` and `loopy--bind-main-body`.
- Add tests.

CHANGELOG.md

@@ -48,6 +48,22 @@ This document describes the user-facing changes to Loopy.
 
 - Better signal an error with conflicting arguments in `numbers`.  See [#172].
 
+- Fix macro expansion in some cases by not resetting the macro environment.
+  For example, we failed to pass the current/modified environment to
+  `macroexpand-all` in some cases.
+
+  ```emacs-lisp
+  ;; Previously failed to use `cl-flet''s internally defined function
+  ;; for `10+':
+  ;; => (11 12 13 14 15)
+  (loopy (named outer)
+         (list i '((1 2) (3 4) (5)))
+         (loopy-iter (listing j i)
+                     (cl-flet ((10+ (y) (+ 10 y)))
+                       (at outer
+                           (collecting (10+ j))))))
+  ```
+
 ### Breaking Changes
 
 - Make it an error to re-use iteration variables with multiple iteration

README.org

@@ -56,6 +56,8 @@ please let me know.
    - The non-keyword arguments of =numbers= are deprecated.  Use the keyword
      arguments instead.  A =:test= keyword argument was added, which is more
      flexible and explicit than the non-keyword arguments.
+   - Fixed a problem with macro expansion in some cases for sub-macros
+     that created a new macro environment (e.g., ~cl-flet~).
  - Versions 0.11.1 and 0.11.2: None. Bug fixes.
  - Version 0.11.0:
    - More incorrect destructured bindings now correctly signal an error.