- had incorrect prototype anyway

This should solve #543, once Clara changes are in as well.

In reality, this is a relatively small performance improvement,
especially with the previous improvements removing lots of superfluous
string handling, but still was measurable.

This is sane, because those `const char*`s are given to us by compiler,
from the text area and thus we do not have to manage their lifetimes. We
also never want to change them.

Also moved copy constructor to compiler-generated methods, not sure why
it wasn't -- even before it was the same as a compiler would generate.

* Compilation warnings fix

* Removed unused argument from reportFatal function

* 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.

Catch apparently supports targeting C++03, so use an inline function
instead.

Catch passes ::tolower into std::transform with string iterators.
::tolower has the signature int(int), which triggers a stealth narrowing
warning inside std::transform, because transform calls
*_Dest = _Fn(*_First), which implicitly narrows an int to a char.

For this particular application the narrowing is fine, so explicitly
narrow in a lambda.