constructor from any const char* and std::string

[Raildex]

You can't construct a fixed string from anything other than fixed strings or char[N] where N is the same size as the fixed string's size.
It would be great to have convenience constructors that take any string and just truncate them.

[unterumarmung]

There are 2 cases for such a constructor:

1. The source string is larger than the destination one
2. The source string is smaller than the destination one

In the first situation we can truncate the string.

But I do not understand what we should do in the second one with the rest of the destination string. Fill with '\0'? This is kinda weird.

[Raildex]

std::string has separate size and capacity. I would expect fixed string to be a string of fixed capacity.

[unterumarmung]

std::string has separate size and capacity. I would expect fixed string to be a string of fixed capacity.

As it stated in the documentation, fixstr::fixed_string has the std::array's semantics of fixed size, not capacity.