Multiblock alignment decoding was wrong if
the block size was not aligned with the output alignment.

Also, what we were calling output iterator was really a
forward iterator. Get it right.

Signed-off-by: Luca Fulchir <luker@fenrirproject.org>

Also: CMake flags fix

Signed-off-by: Luca Fulchir <luker@fenrirproject.org>

blocks, sizes, symbols.

Signed-off-by: Luca Fulchir <luker@fenrirproject.org>

Switched to iterators instead of std::vector.

Now it's possible to build the C interface, and
you can use any container you want.

Signed-off-by: Luca Fulchir <luker@fenrirproject.org>