This PR adds four config options to configure whether and how to load
indutny/elliptic: use_indutny_elliptic, external_indutny_elliptic,
indutny_elliptic_path and indutny_elliptic_fetch_options.
Also:
- Use tweetnacl.js instead of indutny/elliptic for curve25519 key generation
- Don't initialize indutny's curve25519, improving performance when using that curve
- Verify NIST signatures using Web Crypto instead of indutny/elliptic when not streaming
- Move KeyPair.sign/verify to ecdsa.js
- Move KeyPair.derive to ecdh.js
- Move keyFromPrivate and keyFromPublic to a new indutnyKey.js file
Starting from two pull requests by @tanx and @Mithgol this commit implement the following:
- add testing of node version 4.2 LTS;
- move testing to the new TravisCI environment that is expected to be more fast;
- parallelize tests making possible to end first and to test more lasting less;
- make possible for browsertests to fail without impacting on the overall result.
