089a1e452d Replace `Vec::from_hex` with `hex!` (Martin Habovstiak)
Pull request description:
This makes the code less noisy and is a preparation for changing it to `const`-based literal. Because of the preparation, places that used variables to store the hex string were changed to constants.
There are still some instances of `Vec::from_hex` left - where they won't be changeable to `const` and where `hex!` is unavailable (integration tests). These may be dealt with later.
See also #1189
Note that while the change appears big it's nearly entirely mechanical, so should be pretty easy to review. (But I don't feel it's `trivial`.)
ACKs for top commit:
apoelstra:
ACK 089a1e452d
tcharding:
ACK 089a1e452d
Tree-SHA512: c55357b8cffc86f8e107c0f8390490ede75948260018f63dc926455700cbcaf422f6ae72444f93943065e6f4ffa4335bee9160a64184ea4f8e91721f30a46ace
98203bc8b3