Now if the error is not too much critical one can use KIS_ASSERT or
KIS_ASSERT_RECOVER macros. These macros check the condition and ask
the user what to do: try to continue or abort the program and see the
backtrace.

These macros can be use in the following way:

KIS_ASSERT(condition);

or

KIS_ASSERT_RECOVER(condition) {
    // the code that recovers your program after a falure
}

There are three shortcuts available:

KIS_ASSERT_RECOVER_BREAK(cond); --- calls 'break;'
KIS_ASSERT_RECOVER_RETURN(cond); --- returns from current function
KIS_ASSERT_RECOVER_RETURN_VALUE(cond, retval) --- returns from the function with some result

WARNING: These asserts are supposed to be present even in NDEBUG mode!
TODO: Implement automatic saving of the document. See the note
      in kis_assert.cpp