Added timer library (util timer).
Modified MQTT to use tiemr library. (it can handle millisecond instead of second)
Added mqtt-connection? procedure. (it was missing)
Added document of (util timer)
Modified real-part to teturn number itself when it's not c complex number (Fixes #78)
Modified = procedure not to use Sg_NumCmp (Fixes #79)
Adding SRFI-114 tests.
Bit of performance turning.
Added argument check.