1. Added an architecture section.
2. Added a configuration / execution sub-section to developer guide.

Minor tweaks and a bunch of missing fixes from `kafka-site` repo.

Author: Guozhang Wang <wangguoz@gmail.com>

Reviewers: Matthias J. Sax <matthias@confluent.io>, Derrick Or <derrickor@gmail.com>, Ewen Cheslack-Postava <ewen@confluent.io>

Closes #2488 from guozhangwang/KMinor-streams-docs-second-pass

Based on:  https://github.com/apache/kafka-site/pull/27

I recommend also merging into 10.1.0.0 branch to avoid mishaps when re-publishing docs.

Author: Gwen Shapira <cshapi@gmail.com>

Reviewers: Guozhang Wang <wangguoz@gmail.com>

Closes #2077 from gwenshap/protocol_doc_fix

This PR fixes 8 typos in HTML files of `docs` module. I wrote explicitly here since Github sometimes does not highlight the corrections on long lines correctly.
- docs/api.html: compatability => compatibility
- docs/connect.html: simultaneoulsy => simultaneously
- docs/implementation.html: LATIEST_TIME => LATEST_TIME, nPartions => nPartitions
- docs/migration.html: Decomission => Decommission
- docs/ops.html: stoping => stopping, ConumserGroupCommand => ConsumerGroupCommand, youre => you're

Author: Dongjoon Hyun <dongjoon@apache.org>

Reviewers: Ismael Juma

Closes #1138 from dongjoon-hyun/KAFKA-3461

Often it is useful to link to a specific header within the documentation. Especially when referencing docs in the mailing lists.

This adds anchors and links for all headers in the docs.

Author: Grant Henke <granthenke@gmail.com>

Reviewers: Jun Rao <junrao@gmail.com>

Closes #498 from granthenke/doc-links

This PR copies the latest kafka docs to kafka repo docs directory. Here I have copied 0.8.3/ directory contents from svn website repo to kafka/docs repository.

Some questions: This PR contains generated javadocs also.  Do we need to copy javadocs here?

Author: Manikumar reddy O <manikumar.reddy@gmail.com>

Reviewers: Gwen Shapira, Ismael Juma

Closes #171 from omkreddy/KAFKA-2425-MOVE-DOCS-TO-KAFKA-REPO