Update segmentation.cpp

Added detailed comments to watershed()
Update segmentation.cpp

removed trailing whitespaces
Implement VideoCapture::get, CvCapture::getProperty, IVideoCapture::getProperty as constant methods.
SymmRowSmallVec_8u32s [1, 2, 1]
NEON speedup: 4.1
Auto-vect speedup: 2.25
SymmRowSmallVec_8u32s 1x3 general
NEON speedup: 2.56x
Auto-vect speedup: 1.26x

Test kernel: [1, 3, 1]
SymmRowSmallVec_8u32s 1x5 general
NEON speedup: 3.86x
Auto-vect speedup: 1.67x

Test kernel: [0.0708, 0.2445, 0.3694, 0.2445, 0.0708]
SymmRowSmallVec_8u32s [-1, 0, 1]
NEON speedup: 1.84x
Auto-vect speedup: 1.2x
SymmRowSmallVec_8u32s 1x3 asymmetric
NEON speedup: 1.95x
Auto-vect speedup: 1.17x

Test kernel: [-2, 0, 2]
SymmRowSmallVec_8u32s 1x5 asymm
NEON speedup: 3.14x
Auto-vect speedup: 1.6x

Test kernel: [-5, -2, 0, 2, 5]
SymmColumnVec_32s8u
NEON speedup: 1.96x
Auto-vect speedup: 1x

Test kernel: [0.0708, 0.2445, 0.3694, 0.2445, 0.0708]
SymmColumnVec_32s8u asymm
NEON speedup: 2.95x
Auto-vect speedup: 1x

Test kernel: [-0.9432, -1.1528, 0, 1.1528, 0.9432]
SymmColumnSmallVec_32s16s [1, 2, 1]
NEON speedup: 2.66x
Auto-vect speedup: 1x
SymmColumnSmallVec_32s16s [1, -2, 1]
NEON speedup: 2.75x
Auto-vect speedup: 1.01x
SymmColumnSmallVec_32s16s [3, 10, 3] Scharr
NEON speedup: 2.04x
Auto-vect speedup: 1x
SymmColumnSmallVec_32s16s 3x1
NEON speedup: 1.75x
Auto-vect speedup: 1x
SymmColumnSmallVec_32s16s [-1, 0, 1]
NEON speedup: 3.27x
Auto-vect speedup: 1.01x
SymmColumnSmallVec_32s16s 3x1 asymm
NEON speedup: 2.12x
Auto-vect speedup: 1.01x

Test kernel: [-2, 0, 2]
SymmColumnVec_32f16s
NEON speedup: 8.64x
Auto-vect speedup: 1x

Test kernel: [0.1, 0.2408, 0.3184, 0.2408, 0.1]
SymmColumnVec_32f16s asymm
NEON speedup: 9.46x
Auto-vect speedup: 1x

Test kernel: [-0.9432, -1.1528, 0, 1.1528, 0.9432]
SymmRowSmallVec_32f 1x5 
NEON speedup: 2.36x
Auto-vect speedup: 2.36x

Test kernel: [0.1, 0.2408, 0.3184, 0.2408, 0.1]