doc/technical/elemental-deviation: new doc file

Document protocol changes between vanilla TS6 and Elemental-ircd TS6.
The changes are very minimal and will not likely affect day to day
performance of the IRC daemon, but are still worth mentioning.
doc/technical/elemental-deviation: Add information about elemental's use of global SNOMASKs
Merge pull request #27 from lyska/elemental-protocol-deviations

[Documentation] doc/technical/elemental-deviation: new doc file