Update racherdAsync.hpp

Added a more secure threading. This prevents the server from crashing when too many connections occur at once. It also scales better than node.js:
node.js Percentage of the requests served within a certain time (ms)
  50%     77
  66%    122
  75%    213
  80%    333
  90%   1061
  95%   1098
  98%   1317
  99%   3070
 100%   3741 (longest request) - over 3.5 second increase in response time when server is overloading

with this:
Percentage of the requests served within a certain time (ms)
  50%    923 - sure this is slower, but it scales better
  66%    991
  75%   1062
  80%   1110
  90%   1467
  95%   1635
  98%   1806
  99%   1839
 100%   1878 (longest request) - notice how it is almost 2 seconds faster
So this sort of paces the response times allowing the server to be more efficient.