Cargo test fails with the default feature

[ssfdust]

❯ cargo test
   Compiling compio v0.5.0 (/home/ssfdust/Programming/develop/rust/compio)
error[E0432]: unresolved import `compio::event`
 --> tests/event.rs:1:13
  |
1 | use compio::event::Event;
  |             ^^^^^ could not find `event` in `compio`

For more information about this error, try `rustc --explain E0432`.
error: could not compile `compio` (test "event") due to previous error

The event feature seems to the basic feature, how about enabling it on default?

[Berrysoft]

I prefer not enabling it by default:)

I admit that I didn't care about the fails with the default feature. It could be fixed by adding some cfgs, but I didn't do it.

[ssfdust]

No problem, I added it.

[Berrysoft]

Would you open a new PR to add this?

[DXist]

I think it's a good idea to include a CI test run with only default features enabled - I'm personally interested in Linux/mio.