Make vector operators < and > use lexicographical order
Make sure to write SMILES ring bonds canonically
Fix bug in extended_connectivities
Improve canonicalize performance
Merge branch 'master' of https://github.com/timvdm/helium

Conflicts:
	src/smiles.h
	src/util/vector.h
Improve canonicalization performance 2
Add bond order sum as atom invariant
Add support for masked ordered DFS
Update canonical unit test from working on improving performance