Release Version 3.0

[TimNN]

This (currently WIP) PR is a complete reimplementation of cargo-lipo (what 2.0 should have been originally).

The main new features are:

• Reimplementation following current best-practices, including a switch to the 2018 edition.
• Use cargo_metadata to understand the project rather than some custom logic.
• Automatically remove environment variables that can cause issues with build scripts.
• Simplify integration with XCode build scripts: Automatically discover targets and profile from the environment.

This PR is still missing some tests (the basic functionality was manually tested, the XCode integration not at all).

Todo:

• Add tests for:
  • Building a simple project
  • Building a workspace with multiple packages, only some of which are staticlibs
  • Building only specific packages in a workspace
  • Building a package with a build script and dependencies with build scripts
• Improve CI:
  • Run & enforce no-warnings clippy
  • Run & enforce no-diff rustfmt
• Improve Readme.md:
  • Document important options
  • Document XCode integration

Fixes #22.

[eoger]

Automatically remove environment variables that can cause issues with build scripts.

Does this mean I can probably get rid of nenv uses?

[TimNN]

Automatically remove environment variables that can cause issues with build scripts.

Does this mean I can probably get rid of nenv uses?

Yes, once this PR is merged, this should mean exactly that!

[TimNN]

@eoger:

Does this mean I can probably get rid of nenv uses?

I've just published version 3.0, which has the sanitization logic. If you're still having issues, I would love to hear about that.