v0.2.0 released

[anakrish]

Key highlights of this release are:

• no_std support. Regorus can be used in C freestanding environments which don't have the standard C library. no_std can be activated by disabling the default-features. Most functionality works in no_std. For a full list of supported features see regorus/Cargo.toml.
  Thanks @mkulke for guiding this.
• Bindings have been updated and are locked-down with tests. Thanks @thedavemarshall for kickstarting this.
• Kata containers usecase locked down with more tests. Thanks @danmihai1
• Engine API tweaks based on suggestion from @lquerel

Due to the support for no_std, this release is considered a major release. Most clients should see no change.
Clients that disabled default-features and manually specified features might want to consider specifying std regorus feature that will enable std feature in rand and serde_json dependencies.