clean multi-threading macro
fix bug of assign data
Merge pull request #606 from huili2/PredUT_fix

fix bug of assign data of UT code
Add EncoderMB UT test file, and reformat UT files.
Merge pull request #607 from ganyangbbl/encUT_EncoderMB2

Add EncoderMB UT test file, and reformat encoder UT files.
Merge pull request #605 from volvet/clean_mt_macro

clean multi-threading macro
    use function pointer in reference frame management
Merge branch 'vp_dpb' of https://github.com/ruil2/openh264 into vp_update2
add reference frame managment for screen content [still in progress]