Paper: add last points in 7.2
Merge branch 'master' of https://github.com/nicolas-fricke/semmul2013-group1
Paper: add todo in section 7.2.
Paper: add short explanation of hierarchical clustering in section 4.3
Merge branch 'master' of https://github.com/nicolas-fricke/semmul2013-group1
Paper: add cite for hierarchical clustering in section 4.3