Use Option[int] instead of Option[string] for contentLength

[ire4ever1190]

Tested with this and it all seems to work properly

import options, asyncdispatch

import src/httpx

proc onRequest(req: Request): Future[void] =
  if req.httpMethod == some(HttpGet):
    case req.path.get()
    of "/":
      req.send("Hello World")
    of "/customLength":
      req.send(Http200, "Test", contentLength = some 10)
    else:
      req.send(Http404)

run(onRequest)

Has an overload for using Option[string] so old code isn't broken but is marked deprecated so people use the newer version

[ringabout]

Thank you!