A big refactor for the documetations

[Justin Ling Mao <ma...@sina.com>]

Hi gugs:I'am working on doing a big refactor for the documetations.it aims to  - 1.make a better reading experiences and help users know more about zookeeper quickly,as good as other projects' doc(e.g redis,hbase). - 2.have less changes to diff with the original docs as far as possible. - 3.solve the problem when we have some new features or improvements,but cannot find a good place to doc it.
The new catalog may looks kile this:	* is new one added.	** is the one to keep unchanged as far as possible.	*** is the one modified.--------------------------------------------------------------|---Overview    |---Welcome ** [1.1]    |---Overview ** [1.2]    |---Getting Started ** [1.3]    |---Release Notes ** [1.4]|---Developer    |---API *** [2.1]    |---Programmer's Guide ** [2.2]    |---Recipes *** [2.3]    |---Clients * [2.4]    |---Use Cases * [2.5]|---Admin & Ops    |---Administrator's Guide ** [3.1]    |---Quota Guide ** [3.2]    |---JMX ** [3.3]    |---Observers Guide ** [3.4]    |---Dynamic Reconfiguration ** [3.5]    |---Zookeeper CLI * [3.6]    |---Shell * [3.7]    |---Configuration flags * [3.8]    |---Troubleshooting & Tuning  * [3.9]|---Contributor Guidelines    |---General Guidelines * [4.1]    |---ZooKeeper Internals ** [4.2]|---Miscellaneous    |---Wiki ** [5.1]    |---Mailing Lists ** [5.2]--------------------------------------------------------------
The Roadmap is:1.(I pick up it : D)  1.1 write API[2.1], which includes the：     1.1.1  original API Docs which is a Auto-generated java doc,just give a link.    1.1.2. Restful-api (the apis under the /zookeeper-contrib-rest/src/main/java/org/apache/zookeeper/server/jersey/resources)  1.2 write Clients[2.4], which includes the:       1.2.1 C client       1.2.2 zk-python, kazoo      1.2.3 Curator etc.......      look at an example from: https://redis.io/clients

2. write Recipes[2.3], which includes the:  - integrate "Java Example" and "Barrier and Queue Tutorial"(Since some bugs in the examples and they are obsolete，we may delete something) into it.  - suggest users to use the recipes implements of Curator and link to the Curator's recipes doc.
3. write Zookeeper CLI[3.6], which includes the:  - about how to use the zk command line interface [./zkCli.sh]    e.g  ls /; get ; rmr;create -e -p etc.......  - look at an example from redis: https://redis.io/topics/rediscli
4. write shell[3.7], which includes the:   - list all usages of the shells under the zookeeper/bin. (e.g zkTxnLogToolkit.sh,zkCleanup.sh)
5. write Configuration flags[3.8], which includes the:   - list all usages of configurations properties(e.g zookeeper.snapCount):    - move the original Advanced Configuration part of zookeeperAdmin.md into it.     look at an example from:https://coreos.com/etcd/docs/latest/op-guide/configuration.html   6. write Troubleshooting & Tuning[3.9], which includes the:   - move the original "Gotchas: Common Problems and Troubleshooting" part of Administrator's Guide.md into it.   - move the original "FAQ" into into it.   - add some new contents （e.g https://www.yumpu.com/en/document/read/29574266/building-an-impenetrable-zookeeper-pdf-github）.   look at an example from:https://redis.io/topics/problems   		                          https://coreos.com/etcd/docs/latest/tuning.html
7. write General Guidelines[4.1], which includes the:  - move the original "Logging" part of ZooKeeper Internals into it as the logger specification.  - write specifications about code, git commit messages,github PR  etc ...    look at an example from:    http://hbase.apache.org/book.html#hbase.commit.msg.format

8. write Use Cases[2.5], which includes the:  - just move the context from: https://cwiki.apache.org/confluence/display/ZOOKEEPER/PoweredBy into it.  - add some new contents.(e.g Apache Projects:Spark;Companies:twitter,fb)
--------------------------------------------------------------BTW:- Any insights or suggestions are very welcomed.After the dicussions,I will create a series of tickets(An umbrella)- Since these works can be done parallelly, if you are interested in them, please don't hesitate,just assign to yourself, pick it up. (Notice: give me a ping to avoid the duplicated work).