Previously a mismatched prefix would be skipped before the actual
comparison would be performed. Obviously, it is supposed to be
_matching_ prefix that is skipped.

The StringMaker is off by default and can be enabled by a new macro `CATCH_CONFIG_ENABLE_VARIANT_STRINGMAKER`, to avoid increasing the footprint of stringification machinery by default.

Fixes #1375

The desired behaviour was to match a literal "[.]", so the regex
has to be escaped as "\\[\\.\\]" -- double backslashes, because
it has to be escaped from CMake as well as from the regex engine.

This means

* Adding new configuration toggle `CATCH_CONFIG_DISABLE_EXCEPTIONS`
and a best-guess configuration auto-checking for it.
* Adding new set of internal macros, `CATCH_TRY`, `CATCH_CATCH_ALL`
and `CATCH_CATCH_ANON` that can be used in place of regular `try`,
`catch(...)` and `catch(T const&)` respectively, while disappearing
when `CATCH_CONFIG_DISABLE_EXCEPTIONS` is enabled.
* Replacing all uses of `throw` with calls to `Catch::throw_exception`
customization point.
* Providing a default implementation for the above customization point
when `CATCH_CONFIG_DISABLE_EXCEPTIONS` is set.
* Letting users override this implementation with their own.
* Some minor changes and ifdefs all around to support the above