With a "+" or "-" prefix, the "metadata_to_use" setting can manipulate
the existing default.  This way, one can enable `TAG_COMMENT` without
having to list all the other tags.

Add link to more recent libsidplayfp and correct URL pointing to libsidplay2.

Closes #89

Will allow more complex fitler expression, such as negation (#89).

Was converted to reStructuredText / Sphinx in commit
8a689e68

Migrating from DocBook to Sphinx.  Editing XML is really too
cumbersome.

This is an experimental draft.  More needs to be done.

Remove another dependency on the config/Global library.

Closes #296

Moving some text from the manpage.  Oh, documentation is still a mess.