Add more concurrent example/document/blog

[zw963]

e.g. https://lbarasti.com/post/select_statement/, i thought we should add it into official blog.

AFAIK, we even never mention any example/document for select in crystal book or API or official blog.

I consider following examples probably is a good start which i discuss with @Blacksmoke16 on here

ch = Channel(Int32).new
terminate = Channel(Nil).new
done = Channel(Nil).new

[1, 2, 3].each do |i|
  spawn do
    ch.send i
  end
end

spawn do
  loop do
    select
    when value = ch.receive
      p value
    when terminate.receive?
      break
    end
  end
  done.close
end

terminate.close
done.receive?

ch = Channel(Int32).new

[1, 2, 3].each do |i|
  spawn do # => NOTICE: spawn 3 fiber here.
    ch.send i
  end
end

loop do
  break if ch.closed?

  select
  when value = ch.receive?
    p value
  when timeout 3.seconds
    puts "Timeout"
    ch.close
  end
end

[Blacksmoke16]

Duplicate of #208