Prepared Soywiki::Html for substitute templates.

Preparation of Soywiki and Soywiki::Html
for use of alternative templates which
are supposed to be provided through
the commandline/shell.
correct setting of substitute constants.
adding cmdline-switch support for templates.

Switched from the old (static) option-parsing
system to getoptlong option parsing,
to support setting of substitute templates,
while cleaning the option-parsing system.
add usage-info on new cmdline switches.
Merge pull request #23 from 0robustus1/master

Supply own templates