Support running example targets

[yuhr]

In my sandbox project I put hello.rs containing a main function in the examples directory, and I can confirm cargo run --example hello works, but trycmd just ignores test cases that start with $ hello, probably due to #105. Would be good if it supports example targets.

[epage]

We do support examples today; they just aren't automatic due to limitations of cargo (bins are built automatically, examples aren't). See clap as an example of how to register examples

[yuhr]

Thank you for pointing out, the example is illuminating! It seemed to be already documented but I couldn't reach to that file until you told me, so IMHO linking directly to tests/examples.rs file in the documentation would be more helpful.