fixes #45 add cosine similarity; other minor fixes

Performance not bad.

Compare BL and LR models:

Precision means:  0.78567200746 0.954206911202
Recall    means:  0.734577387486 0.953594950604
F-scores  means:  0.746754321281 0.953675692143

Precision - Paired t-test: t=-70.4747052618, p=1.17856855978e-13
Recall    - Paired t-test: t=-88.6723043477, p=1.49536221115e-14
F-score   - Paired t-test: t=-83.3883810466, p=2.5979028457e-14

Compare BL and DT models:

Precision means:  0.78567200746 0.918097581057
Recall    means:  0.734577387486 0.917672886937
F-scores  means:  0.746754321281 0.917723419455

Precision - Paired t-test: t=-50.2089373038, p=2.47462759727e-12
Recall    - Paired t-test: t=-67.0952922136, p=1.83271094959e-13
F-score   - Paired t-test: t=-62.9563868503, p=3.24700452086e-13

Compare BL and SVM models:

Precision means:  0.78567200746 0.925258744902
Recall    means:  0.734577387486 0.921048298573
F-scores  means:  0.746754321281 0.921956946735

Precision - Paired t-test: t=-66.1487003956, p=2.08222850736e-13
Recall    - Paired t-test: t=-92.1417697406, p=1.05895988743e-14
F-score   - Paired t-test: t=-87.7745650205, p=1.63862062362e-14

Compare LR and DT models:

Precision means:  0.954206911202 0.918097581057
Recall    means:  0.953594950604 0.917672886937
F-scores  means:  0.953675692143 0.917723419455

Precision - Paired t-test: t=33.803769453, p=8.55550255774e-11
Recall    - Paired t-test: t=34.3247724956, p=7.46244372884e-11
F-score   - Paired t-test: t=34.1911739665, p=7.72713487038e-11

Compare LR and SVM models:

Precision means:  0.954206911202 0.925258744902
Recall    means:  0.953594950604 0.921048298573
F-scores  means:  0.953675692143 0.921956946735

Precision - Paired t-test: t=22.522948725, p=3.17684023966e-09
Recall    - Paired t-test: t=24.3538730377, p=1.58854216054e-09
F-score   - Paired t-test: t=23.9657073145, p=1.83202598243e-09

Compare DT and SVM models:

Precision means:  0.918097581057 0.925258744902
Recall    means:  0.917672886937 0.921048298573
F-scores  means:  0.917723419455 0.921956946735

Precision - Paired t-test: t=-5.8377699189, p=0.000247505046138
Recall    - Paired t-test: t=-2.87083479, p=0.0184515734061
F-score   - Paired t-test: t=-3.56313750104, p=0.00608929416352