Adding async to zmq package

[Clonkk]

• The async proc were already done by @jackhftang but added to the examples folder and thus not accessible (which is a shame beause it's very useful).
• Added std/ prefix before import.
• Fix a missing a close in examples that could cause CI to hang indefinitely apparently not fixed
• Added runnable exmaples instead of code block and added examples in the documentation
• Added CI to generate docs -> @Araq At your leisure, this requires :
  • creating gh-pages branch
  • enabling github pages for the gh-pages branch on the docs folder.
  • Adding link to the docs in relevant places such as website repo, readme etc.
  • The result can be seen in my fork https://clonkk.github.io/nim-zmq/zmq.html.

=> If you don't want to generate the docs, this can be removed from this PR.

• Bump to version v1.1.0

[Clonkk]

For some reason (I thought I fixed it, but apparently not) the CI sometimes fails and hang indefinitely. I'll reopen this when I can do something. I'll reopen when it's fixed on my fork.

[Clonkk]

Apparently closing PR do not cancel associated jobs so https://github.com/nim-lang/nim-zmq/actions/runs/1067646494 will probably have to be cancelled manually.

Network testing on github CI is volatile; since running the examples wasn't really necessary so I ended making sure the examples compile but without running them.

[Clonkk]

Should the async proc be called sendAsync receiveAsync or æsyncSend, asyncReceive to be consistent with other async package ?

[jackhftang]

@Clonkk I have no opinions on naming. There reasons why I put the procs in /test as an example and aside from zmq is that it makes asyncdispatch module as a required dependence. It seems to me that not everyone use (or like) std/asyncdispatch as their async task runner. And it is easy to copy-and-paste if users have read the examples.

[Araq]

I have no opinion on the names either.