remez.jl: update to work with Julia 1.0.

This program was originally developed for a much earlier version of
Julia, and there have been a lot of changes to Julia semantics since
then. But 1.0 is intended to be stable, so updating once to work with
that should mean that no further updates are needed for a long time.

Changes relevant to this script include new API calls for making
arrays, evaluating Julia source-code expressions from strings, and
parsing strings as numbers; scope and semantics changes requiring
extra escaping in the @debug macro and some explicit 'global' to allow
for-loops to update variables outside themselves; a syntax change for
tuple types; and replacing 'beginswith' on strings with 'startswith'.

There are a couple of remaining inconveniences with this version of
the code. Firstly, the standard Julia 1.0 interpreter will consume a
"--" option terminator on its command line even if it appears after
the script name, so commands of the form 'julia remez.jl -- -1 1 ...'
that worked in Julia 0.2 will no longer work. Adding an extra "--"
before the script name works around this ('julia -- remez.jl -- ...')
because the first "--" is seen by the Julia interpreter and the second
goes to the script. But unfortunately that "--" can't be put in the #!
line as well as the 'env', because of #! command line semantics. So
users may have to work around this by explicitly invoking the
interpreter.

Secondly, Julia 1.0 has moved some mathematical functions (e.g. erf
and gamma) out of its core library into the SpecialFunctions package,
so any pre-existing command lines that used those functions will now
need to qualify them with a package name, and be run on a Julia
installation which has that package installed.

Because Julia 0.4.x is still common (Ubuntu 16.04 and 18.04 both
provide 0.4.5), I've included some backwards-compatibility code so
that the script still runs on that version as well.