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.
Thanks to the changes to compilation model, the tests for benchmarking
macros have been made part of the normal test run. This means that
the only purpose these separately compiled tests served was to waste
CI time.
Now that Catch2 is a proper library, we can always build the full
library (comparatively minor slowdown) and the user can avoid
including benchmarking headers to avoid the compilation slowdown.
When running tests in parallel, CTest runs the tests in decreasing
order of cost (time required), to get the largest speed up from
parallelism. However, the initial cost estimates for all tests are
0, and they are only updated after a test run. This works on a dev
machine, where the tests are ran over and over again, because
eventually the estimates become quite precise, but CI always does
a clean build with 0 estimates.
Because we have 2 slow tests, we want them to run first to avoid
losing parallelism. To do this, we provide them with a cost estimate
manually.
Now that the recommended distribution and usage method is proper
library, users can just avoid including the matcher headers to get
basically the same effect.
