Small typo
Add reference implementation links

This BIP is really hard to implement because of the lack of test vectors and lack of documented  implementations. This will save time for implementers.
Add BitcoinJ excellent introduction
Merge pull request #67 from NicolasDorier/patch-2

Add reference implementation links
Clarify handling of default fields for signing.
Merge pull request #59 from Telepatheic/patch-1

Small typo
bip-0044: scan just external chains