add some enumeration to the list

[eMarchenko]

I'm working on classification of smart contract vulnerabilities. It would be so helpful if I could link to the items using some short tag like SP-2. Currently I have little choice other than use names of those items (like Arithmetic Over/Under Flows).

[AgeManning]

I've added numbers to each list item. I've added references, SP-1, SP-2 etc.. for each enumerated item. Let me know if this doesn't fit your needs.

[eMarchenko]

Well links have just stopped working.
Please check them (e.g. SP-6).

[AgeManning]

The html links are designed to work for the blog post (which has better formatting) not the github readme.
See e.g SP-6