Rework the config developers reference

- Remove redundant language. Focus on the key functions / classes and their inputs
- Add an example for registerNetworkValue()
- Describe the behaviour difference of private values
- Consistently use `plugins.WorldDom.attackTargets.air` in examples (previously it was inconsistent with `plugins.WorldDom.air`)
- Format types with :class:
- Remove fallback code for supybot / gribble. These are Py2-only and unlikely to be relevant these days

use/capabilities.rst

@@ -68,6 +68,7 @@ toggling access for all commands on a global or per-channel level. See the
 :ref:`Example section <capabilities-example>` for some examples on how to do
 this.
 
+.. _built-in-capabilities:
 Special Built-in Capabilities
 -----------------------------
 
@@ -101,6 +102,7 @@ bot to new networks.
 This capability does not automatically grant access to channel administration
 commands, which is instead included in the following capability.
 
+.. _built-in-capabilities-channel-op:
 #channel,op
 ^^^^^^^^^^^