[docs] publish documentation for the generators

[jmini]

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
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Description of the PR

Fixes #441

The documentation (cli help pages) are published under docs/generators.

3 new scripts are introduced:

• bin/utils/export_generators_readme.sh updates the readme: docs/generators/README.md
• bin/utils/export_generator.sh <generator_name> updates the file: docs/generators/<generator_name>.md
• bin/utils/export_docs_generators.sh updates the complete folder docs/generators

This will stay up to data whit the ensure-up-to-date script (see #80)

[etherealjoy]

@jmini
I am missing the options which are exported by the DefaultCodegen like modelNamePrefix for example.

[jimschubert]

Wrapping in the code blocks makes long descriptions overflow.

I'd recommend as a future improvement to convert options to html definition lists and html escape descriptions.

[jmini]

I am missing the options which are exported by the DefaultCodegen like modelNamePrefix for example.

@etherealjoy : nice catch those are the exports produced by our CLI. Please file a separate issue for that.

I'd recommend as a future improvement to convert options to html definition lists and html escape descriptions.

@jimschubert: I totally agree with you. The current output is better than nothing.

It is a quick win by reusing the CLI ouput and doing small search and replace changes with sed to get a Markdown file that can be displayed in the GitHub and that have some links (for navigation).

[wing328]

👍 I'm sure users (especially the new one) will find the doc helpful