add me function pointers for screen contents
This refine is to remove slice number limitation in the future. The changes contains:
1. add pNalLen in Structure SWelsEncoderOutput to store each nal length
2. rename iNalLengthInByte[MAX_NAL_UNITS_IN_LAYER] to pNalLengthInByte in Structure SLayerBSInfo, the pointer point to pNalLen, like pBSBuf point to pFrameBS.
enable Scroll detection into workflow
Fix QP<18 dequant UT bug at encoder side
This should be UT for QP<12.
Clarify a comment about MSVC parameters to fix building gtest

The temporary bug in gtest has now been fixed, but we still can keep
using the current way of fixing MSVC 2012 builds instead of switching
to the solution used previously.
Merge pull request #856 from mstorsjo/clarify-comment

Clarify a comment about MSVC parameters to fix building gtest
Merge pull request #831 from sijchen/md_merge144

[Encoder ME] Add ME function assignment for Screen Content Coding
Merge pull request #853 from dongzha/FixEncUTDequantBugMaster

Fix encoder dequant Unit Test bug for master
Merge pull request #844 from lyao2/scroll_detection

enable Scroll detection into workflow
add one DYN_SLICE UT case
add a comma
reformat
fix UT case
change comment in encoder option according to issue https://github.com/cisco/openh264/issues/859
set minimum quant as 4 to avoid level code overflow
Merge pull request #842 from ganyangbbl/refine_nal2

Refine Nal length related structure
Merge pull request #858 from sijchen/md_merge145

reformat some missed style and remove unused comments
Merge pull request #864 from ruil2/enc_quant

set minimum quant as 4 to avoid level code overflow
Merge pull request #863 from dongzha/FixEncOptionMaster

change comment in encoder option according to issue cisco#859 for master
Merge remote-tracking branch 'upstream/master' into remove_maxslicenum