This commit was previously split into the following parts to ease
review:
- 2d746f68: replace imports
- 4008f0fd: use ecdsa.Signature
- 849e33d1: remove btcec.S256()
- b8f6ebbd: use v2 library correctly
- fa80bca9: bump go modules
This commit adds a new type to the lnwire package: MilliSatoshi. A
milli-satoshi is simply 1/1000th of a satoshi, and will be used for all
internal accounting when sending payments, calculating fees, updating
commitment state, etc. Two helper methods are added: ToBTC(), and
ToSatoshis() to make manipulation of the values easy.