asn1: adds asn1 implementation
asn1/ecdsa: switch to asn1.js

Removes [now] unusued ECDSA functions parseSig, parseSigCompact and
serializeSig.
message: isolate tests further, remove redundant tests

The signing process does not care about a pubKeyHash, and nor does it
care about the network version on a base58 address string.
What signing does do independently is whether the compact signature has
a compression flag or not.

Variables names were also cleaned up a bit.
message: now network agnostic
index: remove TransactionIn/Out
index: remove unused variable
ECKey: remove *Hex/*Buffer operations

These operations are not complete in their serialization of the
underlying private key; as they miss compression information that is
pertinent to the matching public key.

toWIF/fromWIF should always be preferred.

If serialization of the raw private key is necessary, it is simple
enough to simply do: `priv.D.toBuffer()`.
So this is not a regression in convenience or functionality, just a
stricter subset of overall functionality.
message: add network-based Magic prefix