No matcher actually uses it, and there is no good reason for it,
as the best it can do for user is removing a single indirection
when using the pointer inside the matcher. Given the overhead of
other code that will be running during such time, it is completely
meaningless.

This also fixes compilation for PredicateMatcher<const char*>.

Previously a mismatched prefix would be skipped before the actual
comparison would be performed. Obviously, it is supposed to be
_matching_ prefix that is skipped.

Also adds `Predicate` helper function to create `PredicateMatcher`.
Because of limitations in type inference it needs to be explicitly
typed, like so
`Predicate<std::string>([](std::string const& str) { ... })`.
It also takes an optional second argument for description of the
predicate.

It is possible to infer the argument with sufficient TMP, see
https://stackoverflow.com/questions/43560492/how-to-extract-lambdas-return-type-and-variadic-parameters-pack-back-from-gener/43561563#43561563
but I don't think that the magic is worth introducing ATM.

Closes #1236

DJGPP cross compiler is targeting DOS which does not support POSIX
signals. Probably for the same reason (targeting DOS) this compiler
does not support wide characters.

Closes #1093

Also tests :-)