libmcrypt-dev: char* function signatures

[Ralph Schneider <yoursecretsaresafe@googlemail.com>]

(I have trouble finding the original author of mcrypt, so I'm hoping that Debian will be sufficiently upstream for this query.)

Most of the libmcrypt functions that require a char-string take the string as a pointer to non-const char. I am wondering whether that is deliberate, or whether that is just by oversight. If it is feasible to change the signatures to `const char *`, it would make wrapping the library in a C++ class
much easier, since it would allow using standard C++ idioms (like std::string::c_str()) rather than cumbersome copies to writeable memory or using C-style arrays.

I appreciate all your hard work, and thank you very much!