first function added
added geodesic distance similarity
preferential attachment added
added preferential attachment
used rozygen tmeplate
Merge branch 'work'

Conflicts:
	NAMESPACE
	R/similarity_pref_attach.R
	man/similarity_pref_attach.Rd
small fixes
Added common neighbors
Added cosine similarity
Added Jaccard index
Added sorensen index
Added TO DO list
Added hub promoted/depressed index
Added leich-holme-newman index, local
Added adamic-adar index
Added katz index
Added leicht-holme-newman global index
Added average commute time
Added normalized average commute time
Added travis configuration