Currently there are two parts in this experiment: extra directional intra
prediction modes and the filter intra modes migrated from the nextgen branch.

Several macros are defined in "blockd.h" to provide controls of the experiment
settings. Setting "DR_ONLY" as 1 (default is 0) means we only use directional
modes, and skip the filter-intra modes; "EXT_INTRA_ANGLES" (default is 128)
defines the number of different angles we want to support; setting
"ANGLE_FAST_SEARCH" as 1 (default is 1) means we use fast sub-optimal search
for the best prediction angle, instead of exhaustive search. The fast search
is about 6 times faster than the exhaustive search, while preserving about
60% of the coding gains.

With extra directional prediction modes (fast search), we observe the following
code gains (number in parentheses is for all-key-frame setting):
derflr +0.42%  (+1.79%)
hevclr +0.78%  (+2.19%)
hevcmr +1.20%  (+3.49%)
stdhd  +0.56%
Speed-wise, about 110% slower for key frames, and 30% slower overall.

The gains of filter intra modes mostly add up with the gains of directional
modes. The overall coding gain of this experiment:
derflr +0.94%
hevclr +1.46%
hevcmr +1.94%
stdhd  +1.58%

Change-Id: Ida9ad00cdb33aff422d06eb42b4f4e5f25df8a2a