3f3f30d6c7 Use iter instead of accessing content field (Tobin C. Harding)
6389d1cbb3 Stop using push_slice (Tobin C. Harding)
be163eec99 Use Witness::len instead of accessing field (Tobin C. Harding)
Pull request description:
Prepare `Witness` to be moved to `primitives`.
This is the first three patches out of #3406. Patch 1 and 2 are internal changes, path 3 is also internal but introduces a slight perf hit by doing multiple writes.
ACKs for top commit:
apoelstra:
ACK 3f3f30d6c7 successfully ran local tests
Tree-SHA512: 25e2570a22797dbfa15d6e5af9b72938243192ca264bc5fe82c2f327486e52a73993b3b61ee1161e5d17b01a7f9843960cb4031e6550561de4ecafb9f935e375
f3fbd0e0b9