libuecc v6 (2015/10/25)

* Fixes a bug which might have caused a point's y coordinate to be negated
    in certain circumstances when the point was stored in packed
    representation and loaded again. It is extremely improbable that this
    has ever actually happened, as only a small range of coordinates was
    affected.
* Use stdint types to clarify ABI and add support for systems with
    sizeof(int) < 4 (this is not an ABI break in practise as all systems on
    which libuecc has been used in the past should have int == int32_t)
* Add point negation and subtraction functions
* Rename all point access functions to bear a _legacy suffix (the old names
    are still available, but marked as deprecated)
* Add new point access functions and a new generator point that are
    compatible with Ed25519
