Aggressively inlining the short functions in coding.cc

Summary:
This diff takes an even more aggressive way to inline the functions. A decent rule that I followed is "not inline a function if it is more than 10 lines long."

Normally optimizing code by inline is ugly and hard to control, but since one of our usecase has significant amount of CPU used in functions from coding.cc, I'd like to try this diff out.

Test Plan:
1. the size for some .o file increased a little bit, but most less than 1%. So I think the negative impact of inline is negligible.
2. As the regression test shows (ran for 10 times and I calculated the average number)

    Metrics                                         Befor    After
    ========================================================================
    rocksdb.build.fillseq.qps                       426595   444515    (+4.6%)
    rocksdb.build.memtablefillrandom.qps            121739   123110
    rocksdb.build.memtablereadrandom.qps            1285103  1280520
    rocksdb.build.overwrite.qps                     125816   135570    (+9%)
    rocksdb.build.readrandom_fillunique_random.qps  285995   296863
    rocksdb.build.readrandom_memtable_sst.qps       1027132  1027279
    rocksdb.build.readrandom.qps                    1041427  1054665
    rocksdb.build.readrandom_smallblockcache.qps    1028631  1038433
    rocksdb.build.readwhilewriting.qps              918352   914629

Reviewers: haobo, sdong, igor

CC: leveldb

Differential Revision: https://reviews.facebook.net/D15291