- Overrides added
 - usages of push_back() replaced with emplace_back()
 - Loop variable made const-refernce
 - NULL replaced with nullptr
 - Names used in the declaration and definition unified
 - size() replaced with empty
 - Identical cases merged

This way it is explicit when there is a `StringRef` -> `std::string`
conversion and makes it easier to look for allocations that could
be avoided.

Doing this has already removed one allocation per registered test
case, as there was a completely pointless `StringRef` -> `std::string`
conversion when parsing tags of a test case.

Thanks to @ledvinap for noticing

* Allow quotes in CAPTURE arguments

Fix CAPTURE to handle string and character literals properly

This adds UNSCOPED_INFO macro, creating a log message that is stored
until the end of next assertion or the end of test case, whichever comes
first. These messages are not scoped locally, unlike messages created by
INFO macro.

The previous implemetation was just plain broken for most of
possible uses, the new one should work (even though it is ugly
as all hell, and should be improved ASAP).

Fixes #1436

Because the macro name is compile-time constant, we do not have to
worry about lifetimes and will avoid allocation in case of missing
SSO or long macro name.

This means that only one place needs to work with warnings from
the deprecation of `std::uncaught_exception()` in C++17.

Closes #1162.

Closes #1124