The two changes are
`catch_matchers_templates` -> `catch_matchers_templated` and
`catch_matchers_generic` -> `catch_matchers_predicate`. The former
is mostly cosmetic, but the second was previously significantly
misleading, and as the library is now to be consumed by including
specific headers, this needed to be fixed.
In the future we can expect many more matchers, so let's give them
a place to live.
Also moved matcher-related internal files to `internal` subfolder.
Ideally we should sort out all of our source code, but that will
have to come later.
