Guide for "Coin Splitting" in case of hard fork

This guide should cover several different splitting options that we have seen recently:

1) Most important- how to split coins in the event of a fork with no replay protection ([reference](https://bitcointechtalk.com/how-to-protect-against-replay-attacks-7a00bd2fe52f))
2) Cover how you would have split coins for the Bitcoin Cash fork
3) Opt-in replay protection with [payment to known address](https://bitcointechtalk.com/how-segwit2x-replay-protection-works-1a5e41767103)

For first situation, the three approaches that should be covered:
- Replace by fee
- nLockTime
- Using miners coinbase tx

(some extra info/background [here](https://lists.linuxfoundation.org/pipermail/bitcoin-segwit2x/attachments/20171026/b07794dd/attachment.html))

Start by reviewing the linked references and organize the guide around the three splitting situations named in the issue. Done means the guide explains no-replay-protection splitting with Replace by Fee, nLockTime, and a miners coinbase transaction, plus the Bitcoin Cash fork and opt-in payment-to-known-address approach.

Written by the indexing model from the issue text.