glossary: move definition of chain_hash to BOLT #0

This commit modifies the glossary to add a new entry which defines the
usage of `chain_hash` throughout the remainder of the documents.
Additionally, we now also specify which chain hash we expect for
Bitcoin within the glossary.

This commit also modifies BOLT #2 and #7 to omit the definition of the
expected `chain_hash` value for Bitcoin.

00-introduction.md

@@ -110,6 +110,17 @@ This is version 0.
      MUST support the feature in question, while odd numbers indicate
      that the feature MAY be disregarded by the other endpoint.
 
+
+* `chain_hash`:
+   * Used in several of the BOLT documents, and denotes the genesis hash of a
+     target blockchain. This allows nodes to create and reference channels on
+     several blockchains. Nodes are to ignore any messages which reference a
+     `chain_hash` that are unknown to them.
+
+     For the main chain Bitcoin blockchain, the `chain_hash` value MUST be
+     (encoded in hex):
+     `000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f`.
+
 ## Theme Song
 
 

02-peer-protocol.md

@@ -128,9 +128,7 @@ FIXME: Describe Dangerous feature bit for larger channel amounts.
 #### Requirements
 
 A sending node MUST ensure that the `chain_hash` value identifies the chain they
-they wish to open the channel within. For the Bitcoin blockchain, the
-`chain_hash` value MUST be (encoded in hex):
-`000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f`.
+they wish to open the channel within.
 
 A sending node MUST ensure `temporary_channel_id` is unique from any other
 channel id with the same peer.  The sender MUST set `funding_satoshis`

07-routing-gossip.md

@@ -317,8 +317,6 @@ The following table specifies the meaning of the individual bits:
 The creating node MUST set `signature` to the signature of the
 double-SHA256 of the entire remaining packet after `signature` using its own `node_id`.
 
-For the Bitcoin blockchain, the `chain_hash` value MUST be (encoded in
-hex): `000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f`.
 The creating node MUST set `chain_hash` and `short_channel_id` to match the
 32-byte hash and 8-byte channel ID that uniquely identifies the channel within
 the `channel_announcement` message.