Several updates

[eldruin]

Including:

• Update nix
• Raise MSRV to 1.46.0 due to dependencies. Effectively it has been raised already and so far nobody noticed.
• Fix warnings
• Improvements to Cargo.toml
• Add bors configuration
• Switch to GHA for CI (tested on my fork)

Fixes #56

[rust-highfive]

r? @nastevens

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[bors[bot]]

Timed out.

[eldruin]

One of the names for bors must be wrong but I do not know which one. bors retry

[bors[bot]]

Canceled.

[eldruin]

bors try

[bors[bot]]

try

Build succeeded:

• CI (stable, x86_64-unknown-linux-gnu)
• CI (stable, armv7-unknown-linux-gnueabihf)
• CI-macOS (1.46.0, x86_64-apple-darwin)
• CI (1.46.0, x86_64-unknown-linux-gnu)
• CI-macOS (stable, x86_64-apple-darwin)

[ryankurte]

:+1:

bors r+

[bors[bot]]

Build succeeded:

• CI (1.46.0, x86_64-unknown-linux-gnu)
• CI-macOS (1.46.0, x86_64-apple-darwin)
• CI-macOS (stable, x86_64-apple-darwin)
• CI (stable, armv7-unknown-linux-gnueabihf)
• CI (stable, x86_64-unknown-linux-gnu)