Make disabled log prints not compute the string to log

[ailrst]

Currently I log calls eagerly evaluate their parameters, causing wasted work for log calls to levels below the currently enabled log level. This is especially a problem if we compute many large expensive strings just to throw them away.

We can refactor the logger to lazily evaluate its parameters instead:

scala>
def logDebug(v: => String) = {
            if (level > 1) {
               println("log : " + v)
            } 
       }
scala> level = 0
level: Int = 0
scala> logDebug(s"${println("hello")}")
scala> level = 2
level: Int = 2
scala> logDebug(s"${println("hello")}")
hello
log : ()

refactor the logger to lazily compute the string to log, ideally we can simply