Modernize the repository

[Zarthus]

Essentially:

• update dependencies & make them compile

  • all dependencies are updated to the latest known version
    • this fixes many noted security vulnerabilities in the dependencies
    • 2 critical, 3 high, 9 moderate, 1 low
  • reqwest had to enable the blocking feature
    • let client = reqwest::blocking::Client::new();

• rust 2021 edition

  • replace try! macro with ? operator

• bump version to 0.4.0

I also accidentally ran cargo fmt on src/http.rs, sorry about that.
The meat is let client = reqwest::blocking::Client::new();

All tests pass except for these three integration tests - but they also fail on the current master:

failures:
    tests::section_content
    tests::sections
    tests::sections2