* 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.

Now if we detect C++11 compiler, or MSVC in version corresponding to VS2015,
we switch from using `std::random_shuffle` to `std::shuffle`.

`std::random_shuffle` was officially deprecated in C++14, and removed in C++17.

Also removed guarded inclusion of `<random>` header, as there was nothing
in the header that used it.

Catch passes an RNG which accepts int to random_shuffle. Inside
random_shuffle, the STL tries to call that RNG with the difference_type
of the user provided iterators. For std::vector, this is ptrdiff_t,
which on amd64 builds is wider than int. This triggers a narrowing
warning because the 64 bit difference is being truncated to 32 bits.

Note that this RNG implementation still does not produce a correctly
uniformly shuffled result -- it's currently asserting that std::rand
can produce 1000000 which is false -- but I don't know enough about
how much repeatable shuffles are necessary here, so I'm leaving that
alone for now.

Instead of `exit(1)`, it now throws `std::runtime_error` with the details
of the failure. This exception is handled in `run()` at a higher level where
the log is printed to cerr and the test gracefully exits.

- as reported in #545