common Xplor-NIH execution environment

there is one of SimulationWorld object, which can be obtained using the
SimulationWorld_world() function.

The SimulationWorld contains the following infrastructure items:

  timeFactor()        -returns the conversion from the internal time
		       representation to picoseconds.
  kBoltzmann()        -returns the Boltzmann constant in internal units.
  random              -a global instance of the RandomNum class
  setRandomSeed(seed) -method used to reset all random number seeds. 
                       This resets the seed in python's random module,
                       the global RandomNum seed, and the seed used in the
                       XPLOR interface.
  logLevel() / setLogLevel("none" | "normal" | "all" | "debug")
                      -get/set the current logging level. This functionality is
                       not currently utilized much.
  cpuTime()           - return the total CPU time since program start. This
	                time includes that of child processes which have
                        been properly terminated.

The units currently input to xplor-nih are

   length: Angstroms
   time: ps
   energy: Kcal/mol
   mass: atomic-mass-unit
   charge: electron-charge

 physical constants in SI units
 ------------------------------
     Kb = 1.380662 E-23 J/K
     Na = 6.022045 E23  1/mol
     e = 1.6021892 E-19 C
     eps = 8.85418782 E-12 F/m

     1 Kcal = 4184.0 J
     1 amu = 1.6605655 E-27 Kg
     1 A = 1.0 E-10 m

Internally, AKMA units are used:

timeFactor = SQRT ( ( 1A )**2 * 1amu * Na  / 1Kcal )
kBoltzmann = Na *Kb  / 1 Kcal)