Import NETSPLIT and NETJOIN batch type specification by @aji

From https://gist.github.com/aji/02b7edbfefd455365582

Related: #40
extensions/batch: Add batch types, replace example with a specifications section

Related: #40
Make wording of vendor-specific CAP a bit easier.
Fix nested batches, add examples
Merge pull request #46 from DarthGandalf/cap-vendor

Make wording of vendor-specific CAP a bit easier.
Clarify end of batch
index: Added Nefarious IRCu as an IRCv3.1 compatible server
Merge pull request #48 from jobe1986/master

index: Added Nefarious IRCu as an IRCv3.1 compatible server
MONITOR: Reworded issue with WATCH.
Merge pull request #47 from DarthGandalf/batch

Fix nested batches, add examples
Fix ngIRCd link