Breaking changes to do

[lpatiny]

• [x] expose only 2 methods: treeSimilarity(tree, tree, options) and createTree (remove getFunction)
• [x] rename internal method getSimilarity to treeSimilarity (same for test)
• [x] export directly the new treeSimilarity from index.js (no wrap in another function)
• [x] treeSimilarity do not accepts Array of Array (only Tree)
• [x] remove Tree class
• [x] add jsdoc type for Tree
• [x] add correct jsdoc for the methods
• [ ] add more testcases
• [x] createTree should only accept {x:[], y:[]} where x and y are NumberArray (from cheminto-types)
• [x] Adapt the README.md