sim_core: flag equations refactored.

Most flag equations have been refactored into flag group function
  blocks...  The core passes all provided tests in the tests folder
  and now most especially is able to pass the instruction test code.
  At the same time, the overall average cycles per instruction has
  ticked down.

	modified:   sim/sim_core.c
Merge pull request #67 from bsekisser/master-core-refactor-flags

sim_core: flag equations refactored.