3ae21d5111 Use impl_add/sub_assign for block interval (Tobin C. Harding)
9d55922952 Use impl_op_for_references for block height/interval (Tobin C. Harding)
f5e17914b6 Move Assign impls together (Tobin C. Harding)
cc66838e80 units: Remove unnecessary code comments (Tobin C. Harding)
Pull request description:
Improve the ops impls in the `block` module using the already present macros.
ACKs for top commit:
apoelstra:
ACK 3ae21d5111444f5e01f6cfb1a2b9b314f66418a3; successfully ran local tests; nice!
Tree-SHA512: 6565426a06bb47d337d21cf5c59acca43e69228dbec8319fc95373025d220d8ec6273c54f214f312c4229603c455d08e4c6a8c108663c6db5086df36266979de