Fixes #896

`ResultBuilder`s destructor now checks for exceptions, preventing false
negatives. The speedup should remain the same give or take a tiny bit.

Effectively a revert of previous commit, fixing #542, where this was
added to stop linters complaining about `REQUIRE_THROWS_AS` used like
`REQUIRE_THROWS_AS(expr, std::exception);`, which would be slicing the
caught exception. Now it is user's responsibility to pass us proper
exception type.

Closes #833 which wanted to add `typename`, so that the construct works
in a template, but that would not work with MSVC and older GCC's, as
having `typename` outside of a template is allowed only from C++11
onward.

(and ‘expression’, if any, last)
This is a first step towards allowing expression arguments to become variadic

This seems to give about 15% speedup when compiling tests using GCC.

The tradeoff is that under certain circumstances, there is a chance for
false negative result, when the expression under test throws exception
and the test code catches it before it gets to the test runner.

Example:
``` cpp
TEST_CASE("False negative") {
try {
REQUIRE(throws() == "");
} catch (...) {}
}
```
This test case will succeed, reporting no assertions checked, instead of
failing as it would with `CATCH_CONFIG_FAST_COMPILE` disabled. However,
just removing the try-catch block inside client's code will fix this, so
it is worthwhile.

This change does not apply to CHECK* macros, because these are currently
specified as continuing on exception and thus need the local try-catch
to work as intended.