Some of the implementations were inlined instead.

This enables us to avoid `catch_reporter_bases.hpp` being indirectly
dependent on `catch_tostring.hpp`, cutting apart quite a bit indirect
inclusions.

This is first step towards splitting apart reporter implementation
and `catch_string.hpp`.

This should improve the compilation times by decreasing the number
of TUs compiled, without making overly big TUs that would cause
problems with heavy-tailed compilation times.

There is one "combined TU" for the top level part, and each subpart,
except for Reporters, which currently do not have any trivial TUs.

There are two reasons for this:

1) It is highly unlikely that someone has use for this header,
which has no customization points and only provides simplest
possible main, and cannot link the static library which also
provides a default main implementation.
2) It being a header was causing extra complications with
the convenience headers, and our checking script. This would either
require special handling in the checking script, or would break user's
of the main convenience header.

All in all, it is simpler and better in the long term to remove it,
than to fix its problems.

I do not think we need a safeguard against not including files in
CMake anymore, and as it is, it caused annoying false positive about
the default main implementation.