* eql
* equal
* equal-including-properties
* delq
* car-safe
* cdr-safe
* memq
* memql
* member
* nthcdr
* nth
* assq
* assoc
* rassq
* rassoc
* plist-get
* plist-put
* lax-plist-put
* lax-plist-get
* plist-member
* string-equal
* markerp

Other changes:

* Create comparison methods for LispObject for each of the three
  ELisp ways (eq, eql, equal).
* Use the provided way to construct bools and t.
* Create a Rusty API for working with cons cells (as_cons() returns
  a newtype that has car() and cdr() methods).
* Introduce a list tails iterator to replace the FOR_EACH_TAIL and
  FOR_EACH_TAIL_SAFE macro.
* Add missing Cargo.lock for remacs-sys.
* Migrate XXXP() functions to LispObject::is_xxx() and remove unused ones.
* Avoid allocating a vector for each call to a MANY function.
* Fixup makefile targets to avoid "override" warnings.

* Lisp name is inferred from Rust name with underscore -> dash
* C name can be customized in the cases where Rust needs a special name
* Number of args is inferred from Rust. "min" only needs to be given
  if there are optional args.
* Less cloning.

* Use convention LispObject::as_xxx() to get an Optional extracted value.
* Use as_xxx_or_error() to signal a wrong-type-argument if not of that type.
* Move unused CHECK_ macros back to C.
* Move all extern declarations to remacs-sys.

make_number() silently discards the unused bits from EmacsInt
when making a fixnum.