tokio v1

[Tarnadas]

Hey,

here is another attempt at updating tokio to v1.
Some remarks:

• I needed to enable the "rt-multi-thread" feature. Otherwise the tcp server would just block and nothing happens.
• I replaced tokio-serial with serial-io, a custom fork I made based on mio-serial and tokio-serial. It basically just adds tokio v1 support via a feature flag instead of splitting it into different crates. Also all other dependencies have been updated. I checked this PR and made sure that I fixed this.
• serialport-rs changed its interface to a builder pattern, which is why the API of serial-io is slightly different.
• I renamed Serial to AsyncSerial, because the regular Serial in serial-io has no tokio support. I'm not sure, if I should change the name.
• I have only tested the TCP async stuff.

Changelog:

• update tokio to v1
• update bytes to v1
• update tokio-util to v0.6
• replace tokio-serial with serial-io
• add sync rtu client example
• replace example cfg flags with cargo toml required features

closes #71 and #72

[lovasoa]

Hello !
We would need this for our work @enexflow. Let us know if there is anything we can do to help this getting merged :)

@flosse

[Tarnadas]

It looks like Windows support for tokio based serial stuff can be worked on once tokio-rs/tokio#3760 is merged. This would be needed for Modbus RTU. I suppose Windows support should not be dropped from tokio-modbus, thus merging is blocked

[lovasoa]

Hello ! tokio-rs/tokio#3760 was merged and released.
Is there something else that is blocking ?

[ColinFinck]

@Tarnadas I just got the required PR for Windows compatibility into tokio-serial (berkowski/tokio-serial@693e7ee), with a follow-up PR likely to be merged soon (berkowski/tokio-serial#41)
I expect this to be released as tokio-serial 4.4.0

Could you already restructure your PR around that version of tokio-serial?
This would give us an updated tokio-modbus just in time when the tokio-serial update is on crates.io.