* Llama — Compact syntax for short lambda

This package implements a macro named ~##~, which provides a compact way
to write short ~lambda~ expressions.

The signature of the macro is ~(## FN &rest BODY)~ and it expands to a
~lambda~ expression, which calls the function ~FN~ with the arguments ~BODY~
and returns the value of that.  The arguments of the ~lambda~ expression
are derived from symbols found in ~BODY~.

Each symbol from ~%1~ through ~%9~, which appears in an unquoted part
of ~BODY~, specifies a mandatory argument.  Each symbol from ~&1~ through
~&9~, which appears in an unquoted part of ~BODY~, specifies an optional
argument.  The symbol ~&*~ specifies extra (~&rest~) arguments.

The shorter symbol ~%~ can be used instead of ~%1~, but using both in
the same expression is not allowed.  Likewise ~&~ can be used instead
of ~&1~.  These shorthands are not recognized in function position.

To support binding forms that use a vector as ~VARLIST~ (such as ~-let~
from the ~dash~ package), argument symbols are also detected inside of
vectors.

The space between ~##~ and ~FN~ can be omitted because ~##~ is read-syntax
for the symbol whose name is the empty string.  If you prefer you can
place a space there anyway, and if you prefer to not use this somewhat
magical symbol at all, you can instead use the alternative name ~llama~.

Instead of:

#+begin_src emacs-lisp
  (lambda (a &optional _ c &rest d)
    (foo a (bar c) d))
#+end_src

you can use this macro and write:

#+begin_src emacs-lisp
  (##foo %1 (bar &3) &*)
#+end_src

which expands to:

#+begin_src emacs-lisp
  (lambda (%1 &optional _&2 &3 &rest &*)
    (foo %1 (bar &3) &*))
#+end_src

Unused trailing arguments and mandatory unused arguments at the border
between mandatory and optional arguments are also supported:

#+begin_src emacs-lisp
  (##list %1 _%3 &5 _&6)
#+end_src

becomes:

#+begin_src emacs-lisp
  (lambda (%1 _%2 _%3 &optional _&4 &5 _&6)
    (list %1 &5))
#+end_src

Note how ~_%3~ and ~_&6~ are removed from the body, because their names
begin with an underscore.  Also note that ~_&4~ is optional, unlike the
explicitly specified ~_%3~.

Consider enabling ~llama-fontify-mode~ to highlight ~##~ and its special
arguments.