asn1/ecdsa: add prelimary asn1 tests for regression testing
ecdsa: improve BIP62 'low s value' inline comment
ecdsa: P_OVER_FOUR is a curve specific constant
ecdsa: extract BigInteger constants
ecdsa: use square() instead of x*x
ecdsa: clarify comment intention
ecdsa: reduce test vector size

Although reducing a test vector is seemingly a bad thing, we are not
gaining much by having these extra checks, especially since it is
evident that the tests show that there is no repeat k value for:

* Same message, different privateKey
* Different message, same privateKey

The k-values are also matching what is expected, as are the signatures.
bigi: upgrade to 1.1.0
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