This event listener performs basic consistency checks (akin to
matching braces) on events that are passed to the listeners
when the `SelfTest` test binary is run.
The current checks are about nesting events (e.g. `testCaseStarting`
cannot be received before `testRunStarting`, `sectionStarting`
can only be received when a test case is active, etc), and matching
up counts of starting/ended events.
The simplicity means that it could be confused by starting/ended
events matching up but being out of order, e.g.
```
* test case A starting
* test case B ended
* test case B starting
* test case A ended
```
would be accepted, even though it is wrong. However, doing full
order checking would be much more implementation work, for relatively
little benefit, so it is left out for now.
The base was also renamed from `TestEventListenerBase` to
`EventListenerBase`, and modified to derive directly from the
reporter interface, rather than deriving from `StreamingReporterBase`.
Each of the two reporter bases now has its own header file, and
cpp file. Even though this adds another TU to the compilation,
the total CPU time taken by compilation is reduced by about 1%
for debug build and ~0.5% for optimized build of the main library.
(The improvement would be roughly doubles without splitting the TUs,
but the maintainability hit is not worth it.)
The code size of the static library build has also somewhat decreased.
Follow up: Introduce combined TU for reporters, and further split
apart the catch_reporter_streaming_base.hpp header into its
constituent parts, as it still contains a whole bunch of other stuff.
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.
