Add support for using documentation siphons in multiple ways

Experiental support for generating  multiple output formats from the
same siphoned data.

Adds a contrived example to generate a plain list of all CLI commands
(the "itemlist" format).

Eventually we can consider moving the tempate procesisng into the
Output class as well as a way to override how the data is traversed
(ordered).

Change-Id: I77629a74a8fa0c7e583993469dc50491f72f13e7
Signed-off-by: Chris Luke <chrisy@flirble.org>

1 files changed, 130 insertions, 0 deletions

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+{#
+# Copyright (c) 2016 Comcast Cable Communications Management, LLC.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at:
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#}
+# Debug CLI    {{'{#'}}clicmd}
+
+The VPP network stack comes equipped with a set of commands that are useful
+for debugging.
+
+The easiest way to access the CLI (with proper permissions) is to use the
+vppctl command:
+
+```
+sudo vppctl <cli-command>
+```
+
+The CLI parser matches static keyword strings, eventually invoking an action
+function. Unambiguous partial keyword matching always occurs. The action
+functions consume input until satisfied or until they fail. This model makes
+for easy coding, but does not guarantee useful "help" output. It's up to the
+CLI command writer to add useful help strings.
+
+You can find the source code of CLI commands by searching for instances of the
+@c VLIB_CLI_COMMAND macro in the code source files.
+
+Please help maintain and improve this document to make and keep these commands
+clear and useful!
+
+@todo Document where to modify this CLI intro text.
+
+
+## Debug and Telnet CLI
+
+The debug CLI is enabled with the unix interactive parameter or startup
+configuration option. This causes VPP to start without daemonizing and
+presents a command line interface on the terminal where it is run.
+
+The Telnet CLI is enabled with the `cli-listen localhost:5002` option which
+will cause VPP to listen for TCP connections on the localhost address port
+@c 5002. A Telnet client can then connect to this port (for example, `telnet
+localhost 5002`) and will receive a command line prompt.
+
+This configuration will enable both mechanisms:
+
+```
+unix {
+  interactive
+  cli-listen localhost:5002
+}
+```
+
+The debug CLI can operate in line mode, which may be useful when running
+inside an IDE like Emacs. This is enabled with the option
+`unix cli-line-mode`. Several other options exist that alter how this
+CLI works, see the @ref syscfg section for details.
+
+The CLI starts with a banner graphic (which can be disabled) and a prompt. The
+prompt will typically read `vpp` for a release version of VPP and `DBGvpp#`
+for a development version with debugging enabled, for example:
+
+        _______    _        _   _____  ___ 
+     __/ __/ _ \  (_)__    | | / / _ \/ _ \
+     _/ _// // / / / _ \   | |/ / ___/ ___/
+     /_/ /____(_)_/\___/   |___/_/  /_/    
+    
+    vpp# 
+
+versus:
+
+        _______    _        _   _____  ___ 
+     __/ __/ _ \  (_)__    | | / / _ \/ _ \
+     _/ _// // / / / _ \   | |/ / ___/ ___/
+     /_/ /____(_)_/\___/   |___/_/  /_/    
+    
+    DBGvpp# 
+
+This prompt can be configured with the `unix cli-prompt` setting and the
+banner is disabled with `unix cli-no-banner`.
+
+## CLI features
+
+The CLI has several editing features that make it easy to use.
+
+- Cursor keys left/right will move the cursor within a command line;
+  typing will insert at the cursor; erase will erase at the cursor.
+
+- Ctrl-left/right will search for the start of the next word to
+  the left or right.
+- Home/end will jump the cursor to the start and end of the line.
+- Cursor keys up/down and ^P/^N iterate through the command history
+  buffer. Lines from the history buffer may be edited. New commands
+  are added to the end of the buffer when executed; though
+  duplicates of the previous command are not added.
+- ^U erases the line contents from the left of the cursor to the
+  start.
+- ^K erases the contents from the cursor to the end.
+- ^S/^R will search the command history forwards or in reverse for
+  a command; start typing for matches to auto complete.
+- ^L will clear the screen (if supported by the terminal) and repaint
+  the prompt and any current line. The cursor position is also
+  retained.
+- The CLI can be closed with the quit command. Alternatively, ^D on
+  an empty input line will also close the session. Closing the debug
+  session will also shutdown VPP.
+
+Output that exceeds the length of a terminal page will be buffered, up to a
+limit.
+
+- Space or page-down displays the next page.
+- Enter or down-arrow displays the next line.
+- Page-up goes back a page.
+- Up-arrow goes up a line.
+- Home/end jump to the start/end of the buffered output.
+- The key q quits the pager. Space and enter will also quit the
+  pager if the end of the buffer has been reached.
+
+## Index of CLI commands
+
+[TOC]