ecdsa 0.18.0 beta2

changes since 0.18.0-beta1

New features:

• Support for point precomputation for EdDSA.

Maintenance:

• Fix few typos (thanks to Tim Gates and Kian Meng Ang).

Bug fix:

• Accept private EdDSA keys that include public key in the ASN.1 structure.
• Fix incompatibility with Python 3.3 in handling of memoryviews of empty
  strings.