ecdsa: adhere strictly to RFC6979

The previous impl. was in breach of the following section:

> Please note that when k is generated from T, the result of bits2int is
> compared to q, not reduced modulo q. If the value is not between 1 and
> q-1, the process loops.
> Performing a simple modular reduction would induce biases that would be
> detrimental to signature security.
ecdsa: less constant redefinition
ECKey: remove extraneous toString
package: sort lists
ecdsa: ecurve 0.10.0