333c8ab297 Add additional docs to Witness (Tobin C. Harding)
Pull request description:
The `Witness` struct is non-trivial, in particular it is not immediately obvious where and when the compact size encode value for each witness element is stored.
Make an effort to improve the docs on `Witness` in relation to the compact size encoded length of each witness element.
ACKs for top commit:
apoelstra:
ACK 333c8ab297 successfully ran local tests
Kixunil:
ACK 333c8ab297
Tree-SHA512: 1c61a9ad071c035d5ad2e54446120d29ebf8cc4a779c96f04eda825890687dcbd53accc17522f57ef4ffb226eb1d85c6a3a115f27bebcfc7ad3c677033a8a414