core: Update url for issue tracker in error messages

If Waffle encounters an internal error, then direct the user to report
a bug on the issue tracker.

Signed-off-by: Chad Versace <chad.versace@linux.intel.com>
wflinfo: Print all error messages to stderr, not stdout

Some tools interpret messages on stderr as *errors*, and treat stdout
differently, and sometimes ignore stdout completely.

Signed-off-by: Chad Versace <chad.versace@linux.intel.com>
man: run xsltproc with -nonet

This speeds up package builds for debian considerably, but adds
a requirement on the docbook-xsl package.

[chadv] Reduces `ninja man` from 20s to 1.25s.

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Chad Versace <chad.versace@linux.intel.com>