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
* Empty strings are now direct constructed as `std::string()`, not as empty string literals.
* `startsWith` and `endsWith` no longer construct new a string. This should be an improvement
for libstdc++ when using older standards, as it doesn't use SSO but COW and thus even short
strings are expensive to first create.
* Various places now use char literal instead of string literals containing single char.
** `startsWith` and `endsWith` now also have overload that takes single char.
Generally the performance improvements under VS2015 are small, as going from short string
to char is mostly meaningless because of SSO (Catch doesn't push string handling that hard)
and previous commit removed most string handling if tests pass, which is the expect case.
