Support for extended LTC-keys in xprv/xpub format

[nnymsgthb]

Because LTC is natively supported by bitcoinjs-lib I think it is justifiedd to support extended LTC-keys in xprv/xpub format, especially because this format is used by some common wallets (e.g. Jaxx and I believe Exodus). The network definition was taken from @iancolemn (see https://github.com/iancoleman/bip39/blob/master/src/js/bitcoinjs-extensions.js).

[dabura667]

Ugh...

What is the point of standards if no one uses them... sigh

@dcousens perhaps we should allow HDNodes to prefer the network object and only soft-warn if it differs from the standard.

Switching to a soft-warn rather than a hard fail could also (in an ugly way) fix the ypub / zpub problem.

[dabura667]

NACK on the new network idea, though.

[dcousens]

@dabura667 my thoughts was, only enforce the network object strictly if they provide it.
I also don't know if we should bother, users who want to suppory multiple constants can easily use an array of networks...

[dcousens]

@nnymsgthb this isn't the solution to this problem.

For your purposes, you can simply use:

bitcoin.HDNode.fromBase58(..., [bitcoin, litecoin, custom1, custom2]) // or bitcoin.HDNode.fromBase58(..., custom1) 

Where custom is your network object defined above.

[dcousens]

Related #927

[nnymsgthb]

Related #995

[vincenzourbisaglia]

@dabura667 doesn't the litecoin-project define xprv/xpub?
https://github.com/litecoin-project/litecoin/blob/v0.13.2.1/src/chainparams.cpp#L130