Update

[wackbyte]

• Use Cell::from_mut and Cell::as_slice_of_cells rather than using mem::transmute
• Use #![no_std] and core
• Add a Minimum Supported Rust Version (MSRV) of 1.37
  • I decided to choose this version specifically because the Cell functions were stabilized in it
• Migrate from Travis CI to GitHub Actions
  • Note that for the automatic GitHub Pages deployment to work, you will need to:
    • Go to the settings for the repository
    • Find Pages -> Build and Deployment -> Source
    • Set it to "GitHub Actions (Beta)"
• Remove the note at the end of the crate documentation about the likely unsafety of the implementation as that's no longer true
• Fix deprecated license format in Cargo.toml
• Minor formatting changes