emit speed up

[shokai]

ruby 2.0.0-p0 (2013-02-24) [x86_64-darwin12.3.0]
       user     system      total        real
100Kon_1emit  2.910000   0.110000   3.020000 (  3.268702)
1Kon_1Kemit  5.290000   0.030000   5.320000 (  5.593177)
1on_100Kemit  0.830000   0.010000   0.840000 (  0.884736)

ruby 1.9.3-p392 (2013-02-22) [x86_64-darwin12.3.0]
       user     system      total        real
100Kon_1emit  2.500000   0.110000   2.610000 (  2.744506)
1Kon_1Kemit  4.610000   0.020000   4.630000 (  4.828477)
1on_100Kemit  0.840000   0.010000   0.850000 (  0.909776)

ruby 1.9.2-p320 (2012-04-20) [x86_64-darwin12.3.0]
      user     system      total        real
100Kon_1emit  2.440000   0.110000   2.550000 (  2.688111)
1Kon_1Kemit  4.820000   0.030000   4.850000 (  5.053036)
1on_100Kemit  0.690000   0.010000   0.700000 (  0.751837)

ruby 1.8.7-p371 (2012-10-12) [i686-darwin12.3.0]
      user     system      total        real
100Kon_1emit  6.360000   0.470000   6.830000 (  7.210291)
1Kon_1Kemit  9.590000   0.040000   9.630000 ( 10.141170)
1on_100Kemit  1.730000   0.000000   1.730000 (  1.789773)

ruby 1.9.3-p385 (2013-02-21) [java]
       user     system      total        real
100Kon_1emit  6.330000   0.190000   6.520000 (  4.425000)
1Kon_1Kemit  5.540000   0.050000   5.590000 (  5.412000)
1on_100Kemit  0.990000   0.010000   1.000000 (  1.052000)

[shokai]

use Hash instead of Array

ruby 2.0.0-p0 (2013-02-24) [x86_64-darwin12.3.0]
       user     system      total        real
100Kon_1emit  3.130000   0.120000   3.250000 (  3.521551)
1Kon_1Kemit  3.770000   0.040000   3.810000 (  4.099890)
1on_100Kemit  0.790000   0.000000   0.790000 (  0.815189)

ruby 1.8.7-p371 (2012-10-12) [i686-darwin12.3.0]
      user     system      total        real
100Kon_1emit  8.490000   0.570000   9.060000 ( 10.294411)
1Kon_1Kemit  6.010000   0.030000   6.040000 (  6.761206)
1on_100Kemit  1.900000   0.020000   1.920000 (  2.055817)

[shokai]

use 2 Hashes (type, id)

ruby 2.0.0-p0 (2013-02-24) [x86_64-darwin12.3.0]
       user     system      total        real
100Kon_1emit  3.610000   0.130000   3.740000 (  3.945285)
1Kon_1Kemit  3.780000   0.040000   3.820000 (  4.087325)
1on_100Kemit  0.700000   0.010000   0.710000 (  0.764164)

ruby 1.8.7-p371 (2012-10-12) [i686-darwin12.3.0]
      user     system      total        real
100Kon_1emit  9.640000   0.550000  10.190000 ( 10.085752)
1Kon_1Kemit  5.340000   0.030000   5.370000 (  5.743721)
1on_100Kemit  1.580000   0.010000   1.590000 (  1.748632)