RC LOWBR mode merge
avoid QP sudden fluctates
add UT for PredMv in decoder
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
Move the RC_MODES enum to the public header

This allows users to know what values to set for the iRCMode
parameter.
Make the iRCMode field use the RC_MODES type instead of plain int

This makes it even clearer for users about how to set this field.
Merge pull request #561 from mstorsjo/use-rc-enum

Make the RC_MODES enum public, use it for the iRCMode field
Merge remote-tracking branch 'upstream/master' into travis.android