(ffap-alist): Delete `math-mode'.

(ffap-alist): Delete `math-mode'.
Move all defvars and defuns out of this, to top level.
Use a constant list as the initial value.
(ffap-soft-value): Rewrite as a macro.
And now it is used only at run time, not at load time.
(ffap-ftp-default-user): Use just "anonymous" as default value.
(ffap-what-domain): Don't set mail-extr-all-top-level-domains here.
(ffap-newsgroup-regexp, ffap-newsgroup-heads): Move up past first use.
(ffap-string-at-point-region): Likewise.