Improve aleph.http/start-server's docstring for :idle-timeout

Explain what exactly idle means and remove needlessly narrow and
potentially misleading reference to keep-alive connections.

Closes #609.

Author: DerGuteMoritz

src/aleph/http.clj

@@ -49,7 +49,7 @@
    | `epoll?` | if `true`, uses `epoll` when available, defaults to `false`
    | `compression?` | when `true` enables http compression, defaults to `false`
    | `compression-level` | optional compression level, `1` yields the fastest compression and `9` yields the best compression, defaults to `6`. When set, enables http content compression regardless of the `compression?` flag value
-   | `idle-timeout` | when set, forces keep-alive connections to be closed after an idle time, in milliseconds
+   | `idle-timeout` | when set, connections are closed after not having performed any I/O operations for the given duration, in milliseconds. Defaults to `0` (infinite idle time).
    | `continue-handler` | optional handler which is invoked when header sends \"Except: 100-continue\" header to test whether the request should be accepted or rejected. Handler should return `true`, `false`, ring responseo to be used as a reject response or deferred that yields one of those.
    | `continue-executor` | optional `java.util.concurrent.Executor` which is used to handle requests passed to :continue-handler.  To avoid this indirection you may specify `:none`, but in this case extreme care must be taken to avoid blocking operations on the handler's thread."
   [handler options]