v0.3.0: Support for nested crates with binary targets

[rnag]

Closes #19

Changes

Support for Cargo crates with binary targets.

• The Cargo crates would be nested (as sub-folders) within the examples/ folder
• Each crate would contain its own Cargo.toml file
• The crate would normally be run with cargo run, and the default binary target would then be src/main.rs
• For multiple binaries, we could define separate entries for [[bin]] in a crate's Cargo.toml file, and then cargo-rx should display each binary target as a separate example to run