STL-like iterator protocol for vector3

Providing iterator and const_iterator typedefs as well as begin() and
end() methods allow using vector3 with STL algorithms like `for_each` or
`find_if`.
Add CO2H to superatom.txt

I note that CO2H is in osra, just in spelling.txt instead of superatom
Merge pull request #103 from cowsandmilk/CO2H

Add CO2H to superatom.txt
Merge pull request #102 from Synss/vector3-iterators

STL-like iterator protocol for vector3