* remove raw SSE2/NEON implementation from convert.cpp
  * remove raw implementation from Cvt_SIMD
  * remove raw implementation from cvtScale_SIMD
  * remove raw implementation from cvtScaleAbs_SIMD
  * remove duplicated implementation cvt_<float, short>
  * remove duplicated implementation cvtScale_<short, short, float>
  * add "from double" version of Cvt_SIMD
  * modify the condition of test ConvertScaleAbs

* Update convert.cpp

fixed crash in cvtScaleAbs(8s=>8u)

* fixed compile error on Win32

* fixed several test failures because of accuracy loss in cvtScale(int=>int)

* fixed NEON implementation of v_cvt_f64(int=>double) intrinsic

* another attempt to fix test failures

* keep trying to fix the test failures and just introduced compile warnings

* fixed one remaining test (subtractScalar)