support for binding descriptors per channel name

docs/src/main/asciidoc/intro.adoc

@@ -38,7 +38,8 @@ The `application.yml` has the mapping from channel names to external broker hand
 spring:
   cloud:
     stream:
-      outputChannelName: ${spring.application.name:ticker}
+      bindings:
+        output: ${spring.application.name:ticker}
 ----
 
 `@EnableModule` is parameterized by an interface (in this case `Source`) which declares input and output channels. `Source`, `Sink` and `Processor` are provided off the shelf, but you can define others. Here's the definition of `Source`
@@ -76,7 +77,7 @@ NOTE: In this case there is only one `Source` in the application context so ther
 
 == Multiple Input or Output Channels
 
-A module can have multiple input or output channels all defined either as `@Input` and `@Output` methods in an interface (preferrable) or as bean definitions. Instead of just one channel named "input" or "output" you can add multiple `MessageChannel` methods annotated `input.*` or `output.*` and the names are converted to external channel names on the broker. The external channel names are the `spring.cloud.stream.[input|output]ChannelName` plus the `MessageChannel` bean name, period separated. In addition, the bean name can be `input.[queue|topic|tap]:*` or `output.[queue|topic]:*` (i.e. with a channel type as a colon-separated prefix), and the semantics of the external bus channel changes accordingly (a tap is like a topic). For example, you can have two `MessageChannels` called "output" and "output.topic:foo" in a module with `outputChannelName=bar`, and the result is 2 external channels called "bar" and "topic:foo.bar".
+A module can have multiple input or output channels all defined either as `@Input` and `@Output` methods in an interface (preferrable) or as bean definitions. Instead of just one channel named "input" or "output" you can add multiple `MessageChannel` methods annotated `@Input` or `@Output` and the names are converted to external channel names on the broker. The external channel names can be specified as properties that consist of the channel names prefixed with `spring.cloud.stream.bindings` (e.g. `spring.cloud.stream.bindings.input` or `spring.cloud.stream.bindings.output`). External channel names can have a channel type as a colon-separated prefix, and the semantics of the external bus channel changes accordingly (a tap is like a topic). For example, you can have two `MessageChannels` called "output" and "foo" in a module with `spring.cloud.stream.bindings.output=bar` and `spring.cloud.stream.bindings.foo=topic:foo`, and the result is 2 external channels called "bar" and "topic:foo".
 
 == Samples
 
@@ -117,7 +118,7 @@ For an XD module the channel names are `<group>.<index>` and a source (output on
 
 == Taps
 
-All output channels can be also tapped so you can also attach a module to a pub-sub endpoint and listen to the tap if you know the module metadata. To tap an existing vanilla module you need to know its `outputChannelName` and the tap name is then `tap:<outputChannelName>`, so you can listen to it on an input channel named `input.topic.tap:<outputChannelName>`. The tap is only active if you explicitly ask for it: you can do that by POSTing to the HTTP endpoint `/taps/<channelName>` (where the channel name can be the internal or external name, e.g. "output" or the external name mapped to the output channel).
+All output channels can be also tapped so you can also attach a module to a pub-sub endpoint and listen to the tap if you know the module metadata. To tap an existing vanilla module you need to know its `outputChannelName` and the tap name is then `tap:<outputChannelName>`, so you can listen to it on an input channel named `topic.tap:<outputChannelName>`. The tap is only active if you explicitly ask for it: you can do that by POSTing to the HTTP endpoint `/taps/<channelName>` (where the channel name can be the internal or external name, e.g. "output" or the external name mapped to the output channel).
 
 To tap an existing output channel in an XD module you just need to know its group, name and index, e.g.