Bump MSRV to 1.56.1

[tcharding]

As we have done in other parts of the ecosystem bump the MSRV to Rust v1.56.1.

Done for secp256k1 and secp256k1-sys.

This was originally in #688 but there are too many things going on so here it is separately.

[apoelstra]

Should also update clippy.toml and both READMEs.

[tcharding]

Ok, done properly now

git grep '1\.48'
CHANGELOG.md:22: * Bump MSRV to 1.48 [#595](https://github.com/rust-bitcoin/rust-secp256k1/pull/595)
secp256k1-sys/CHANGELOG.md:17: * Bump MSRV to 1.48 [#595](https://github.com/rust-bitcoin/rust-secp256k1/pull/595)

[apoelstra]

Heh, this breaks the vendoring script, which looks for patterns like x.y.z to find the version of secp256k1. Adding rust_version = "1.56.1" causes it to find two values, which derails the rest of the script.

The offending line is line 11 of secp256k1-sys/vendor-libsecp.sh which goes

DEFAULT_VERSION_CODE=$(grep version "$SECP_SYS/Cargo.toml" | sed 's/\./_/g' | sed 's/.*"\(.*\)".*/\1/')

We need to tighten this sed line.

To save you time I asked the chatbot to do it, which gave me

grep version "$SECP_SYS/Cargo.toml" | sed -n 's/version = "\([0-9]\+\.[0-9]\+\.[0-9]\+\)"/\1/p' | tr '.' '_'

which looks a lot more legit than my old code.

[tcharding]

The bot is way better at writing shell that we are - glad I don't depend on writing shell for a paycheck.

[apoelstra]

Lol, yeah. Shell has gotta be the biggest area where I'm not even close to its skill (and don't want to be :P).

[apoelstra]

Oh, but lol, I think in this case it still won't work. I think we need to change the initial grep version to grep '^version =' or something, so it doesn't match on rust_version =.

[tcharding]

The bot was wrong! I used ^ to only match on the start of the line. Not entirely sure if the quotes are needed but it works as is. FTR I was setting this value manually when I ran the script pereviously.

[apoelstra]

Hah, jinx.

[tcharding]

Ha, real time chatting on github.

[tcharding]

jinx again

[apoelstra]

ACK 2d0c783