remove docgen source and targets from build

pkg/docgen/README.md

-docgen
-======
-
-**Deprecated** please use https://pub.dartlang.org/packages/dartdoc instead.
-
-A documentation generator for Dart.
-
-- - -
-The docgen tool takes in a file or directory as input and produces documentation
-for all `.dart` file it finds as YAML or JSON files. This outputs information 
-about all classes, variables, functions, and methods defined in the library and 
-its imported libraries.
-
-### Quick Start: Common Commands 
-
-##### To only generate documentation, while standing in the `bin` directory:
-
-`dartdoc.py` generates all documentation and runs a local server with your html
-pages.
-
-`dartdoc.py -d` ONLY generates documentation for the SDK and all packages (no
-html pages generated and no server).
-
-`dartdoc.py -d -o package/to/document` ONLY generates documenation for the
-specified package.
-
-##### To generate documentation and view it through the webpage:
-- Install [Google App Engine SDK for Python][GAE] (one time setup) and agree to
-   add symlinks so that dev\_appserver.py can be found on your PATH.
-- Run `dartdoc.py`.
-
-### Generating files & uploading to Cloud Storage
-
-The viewer uses YAML files generated by the docgen package as the data 
-being displayed. These files are stored in Google Cloud Storage.
-
- - Run `python upload_docgen.py` to generate these files and upload them to 
- Cloud Storage as a new version.
-- - -
-These tasks can be done separately if necessary:
-
-##### 
-
-#### Generating YAML files
-
-YAML files can be generated using the docgen package in the dart repository. 
-
-###### Usage 
-
-Run  `dart docgen.dart [OPTIONS] <path to directory or file>`
-
-###### Options available
-
-- `-h`, `--help` Prints help and usage information.
-- `-v`, `--verbose` Output more logging information.
-- `-j`, `--[no-]json` Outputs to JSON. Files are outputted to YAML by default. 
-If `--append` is used, it takes the file-format of the previous run stated in 
-library_list.json ignoring the flag.
-- `--include-private` Flag to include private declarations.
-- `--include-sdk` Flag to parse SDK Library files imported.
-- `--parse-sdk` Parses the SDK libraries only. (Ignores the path passed in.)
-- `--package-root` Sets the package root of the library being analyzed.
-- `--append` Appends to the docs folder, library_list.json, and index.txt.
-- `--introduction` Adds the provided markdown text file as the introduction
-for the outputted documentation.
-
-
-###### Output directory
-Documented libraries will be located at bin/docs in either YAML or JSON format 
-depending on options specified. There will also be a library\_list.json, 
-containing a list of all the libraries inside the docs folder. 
-
-To get more information on how to use the outputted documentation with 
-dartdoc-viewer, please take a look at the 
-[dartdoc-viewer documentation][dartdoc-viewer].
-
-#### Uploading to Cloud Storage
-
-To push new files to Google Cloud Storage for use by the viewer, use the 
-`gsutil` tool located at third_party/gsutil/gsutil in the Dart repository.
-
- - Run `python gsutil -m cp -q -a public-read -r <folder> gs://dartlang-docgen`
- to upload the specified folder to the viewer's bucket. Be sure to also upload 
- a new VERSION file if the uploaded folder is to be used.**
-
-**Note that the bucket contains several numbered folders for each version of 
-the documentation. Run `python gsutil ls gs://dartlang-docgen` to see the file 
-layout. Follow this convention and update a new VERSION file when uploading 
-a new version of documentation. You can see the format of the VERSION file 
-by running `python gsutil cat gs://dartlang-docgen/VERSION`.
-
-### Viewing generated documentation
-
-Docgen's generated YAML files can be used by the 
-[Dart Documentation Viewer][dartdoc-viewer] for easy viewing and navigation 
-through a project. 
-
----
-
-#### Using dartdoc.py
-
-The `dartdoc.py` script located in the `bin` directory is a useful tool for 
-creating documentation for a Dart project and running it locally. 
-
-##### Setup
-
-The `dartdoc.py` script makes use of the 
-[Google App Engine SDK for Python][GAE]'s development server to serve the 
-documentation viewer. Install a recent version of the SDK before running 
-`dartdoc.py`.
-
-##### Running dartdoc.py
-
-######Common Options
-
-The following options are the most used:
-
-    python dartdoc.py --gae-sdk=<path to SDK>
-      --options=<path to files>
-      --options=--parse-sdk
-      --options='--include-sdk <path to files>'
-      --options='--append <path to files>'
-
-######All Options
-
-Run `python dartdoc.py -h` from the `bin` directory for all available options. 
-The two required options are as follows:
- 
- 1. The `--options` option describes any options being passed into `docgen.dart`.
- If more then one option is desired, separate the options with a space 
- (ex. `--options='--include-sdk files'`).
- 2. The `--gae-sdk` option gives the absolute path to the 
- [Google App Engine SDK][GAE]. 
-
-Running `python dartdoc.py --options=<docgen options> --gae-sdk=<path to SDK>` 
-will serve files generated by `docgen.dart` in your browser.
-
-[dartdoc-viewer]: https://github.com/dart-lang/dartdoc-viewer "Dartdoc-Viewer"
-[GAE]: https://developers.google.com/appengine/downloads#Google_App_Engine_SDK_for_Python  "Google App Engine SDK for Python"
-