RC LOWBR mode merge
refactor the setting of function pointer for simplification
Add Unit Test Expand Picture
avoid QP sudden fluctates
add static
 add maxbitrate parameter
rephrase blockzero function complexity and remove useless functions
Merge pull request #552 from dongzha/ExpandPic

Add Unit Test Expand Picture
Merge pull request #550 from sijchen/funcptr_refactor

[Encoder Refactor] Simplify the setting of function pointers
Merge pull request #554 from ruil2/encoder_update

 add maxbitrate parameter
Merge pull request #555 from huili2/remove_unused_func

rephrase blockzero function complexity and remove useless functions
add UT for PredMv in decoder
expand MVD table and rename some macros
add leve parameter, update profile and usagetype type
Merge pull request #557 from sijchen/me_refactor4444

[Encoder Refactor] Expand MVD table
Merge pull request #558 from ruil2/encoder_level

add leve parameter, update profile and usagetype type
add uiMaxNalSize to support the maximum nal size setting
Merge pull request #559 from huili2/UT_PredMv

add UT for PredMv in decoder
Merge pull request #549 from lyao2/rc_tune

RC LOWBR mode merge
Merge pull request #560 from ruil2/encoder_nal

add uiMaxNalSize to support the maximum nal size setting