dev-perl/Boulder: Bulk fixes and fix for bug #678004

dev-perl/Boulder: Bulk fixes and fix for bug #678004

- Convert to EAPI6
- Omit Boulder::Store support unless USE=store is specified, as
  Boulder::Store requires DB_File, which requires perl built with
  USE="berkdb", and triggering a perl rebuild flipping a use flag
  could really complicate portage's capacity to solve dependencies,
  and possibly break your perl. (This is exposed bug bug #678004)
- Omit Boulder::Labbase as the module is incomplete, is documented as
  such, and loads dependencies that aren't available on Gentoo or on
  CPAN.
- Omit Boulder::XML and its dependency on XML-Parser unless USE=xml is
  specified, as XML handling is not in any way critical to this module.
- Remove uncondtional compile-time assertion for XML::Parser
- Omit Boulder::Genbank and related assets unless USE=genbank is
  specified, as this necesarily adds a dependency on dev-perl/CGI as
  part of its Entrez accessor
- Provide examples via USE="examples"

Closes: https://bugs.gentoo.org/678004
Package-Manager: Portage-2.3.66, Repoman-2.3.16
Signed-off-by: Kent Fredric <kentnl@gentoo.org>