By using char const * instead of std::string we avoid significant
copying per assertion.  In a simple loop with 10000000 CHECKS on
my system, this reduces the run time from 9.8s to 6s.

Previously, this would not print out any messages for the last CHECK
```cpp
TEST_CASE("Foo") {
INFO("Test case start");
for (int i = 0; i < 2; ++i) {
INFO("The number is " << i);
CHECK(i == 0);
}
CHECK(false);
}
```

now it does.

What an embarassing bug, I'll have to look into why it wasn't caught by
any of Catch's self-tests.

Fixes #885 and closes #887 (duplicate)

Unexpected exceptions no longer cause abort and there should be no more
potential for false negatives.

The trade-off now is that exceptions are no longer translated.

In some cases, like when given

```cpp
std::vector<char>* str =
reinterpret_cast<std::vector<char>*>(0x1234458);
CHECK(*str == std::vector<char>());
```

reconstructing the expression to report it would cause another fatal
error. Instead we just put together an AssertionResult without
reconstructing the expression fully.

This should fully fix #810

It wasn't necessary anyway.
This addresses #821