refactor: be consistent about env being the last argument.

* lib/sexpr/lisp.lua (env_bind, env_push, anv_apply): Rename from
these...
(bind, pushenv, apply): ...to these.
(pushenv): Add optional `init` parameter.
(bind, apply, evalquote, evalargs, evalsexpr, evalstring)
(evalfile): Make `env` the last parameter, defaulting to `obarray`
when unspecified.
Adjust all callers.
* lib/sexpr/primitive.lua (*, +, -, <, car, cdr, cons, consp)
(defmacro, eq, eval, if, lambda, load, progn, setq): Likewise.
* sexpr: Simplify a little.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>