Move templatess to `templates/$action/$engine.tmpl`.

This gives us engine-specific default templates, currently including Postgres
and SQLite templates. The addition of the `--template` option to the `add`
command allows the user to specify a template of any name, which will make
customization much easier.

Still to do:

* Update the docs with the new template names.
* Update the installer to install the templates in the right place.
* Update the installer to move existing templates to subdirectories,
  and emit a message about user- or project-specific custom templates
  needing to be moved, as well.

Ref issue #50.
Add oracle and mysql templates.

The oracle templates are non-transactional.
Document the new --template option and locations.
Move old templates in etc directory.

On install. This is to preserve any customizations that might have been added
in the past. The new file names will be for Postgres and SQLite; The Oracle
template is different, and likely not used by anyone much yet, so don't worry
about it. Don't bother with MySQL, either, since it hasn't been released yet.

Also requires that `process_etc_files()` recognize the old names, so that it
still appends .default. This is because the files are moved on `install`, and
`process_etc_files()` runs on `build`, so the files will not have been moved,
yet.
Notify installer that template locations must be updated.
Note addition of --template-name in Changes.

Closes #50.
Add diagnostic to try to figure out why Travis CI fails.
Emit diagnostics for Travis failure only if RELEASE_TESTING is set.
Add `--exists` to the `show` command.

Closes #59.
Update l10n files.
Timestamp v0.980.
Timestamp spec file.
Require PostgreSQL 8.4.0 in the spec file.
Timestamp v0.980.
Collect values for duplicate add command --set keys into an array.

To be passed as such to the templates, as has always been documented.
Use Template Toolkit for templates, if it's installed.

Closes #51.
Remove diagnostic; actuall *use* Template.
Test both Template::Tiny and Template Toolkit.

The latter only if it is installed. Use a code ref in `@INC` to fool perl
into thinking that Template.pm is not installed.
Try to fix parallel test execution failures.
Mention Template Toolkit upgradability in the docs.