Support @VERSION@ and @SEMVER@ in captcha_cmd option

[badlop]

Those macros are useful because the example captcha scripts are copied in a path ejabberd-$VERSION/priv/bin tha depends on the ejabberd version number, and changes for each release. Also, depending on the install method (one that uses rebar3, or Elixir's mix), that $VERSION may be in XX.YY or in SEMVER format (respectively).

Thanks to @weiss for the semver_to_xxyy/1 function code.

[coveralls]

Coverage decreased (-0.005%) to 33.604% when pulling 217e930 on badlop:captchaversion into fbf43f2 on processone:master.

[Neustradamus]

@badlop: It will be in 22.10?

[badlop]

@badlop: It will be in 22.10?

Finally, yes