Update documentation.

1. Change overview picture.
2. Delete sample code.
3. Add meetup slides link.
Remove DummyLog.
Merge pull request #194 from EasonLiao/rm_dummylog

Remove DummyLog.
Merge pull request #193 from EasonLiao/doc

Update documentation.
Fsync log directory when file gets changed.

https://issues.apache.org/jira/browse/ZOOKEEPER-2003
Specify booting parameters in constructor.
Merge pull request #189 from EasonLiao/initialize

Move the initialization parameter to constructors
Merge pull request #107 from EasonLiao/fsync_dir

Fsync directory when files are changed
User decides when to take snapshot.
Raise exception if the size of pending req is large.

Before we blocked the send method.
Merge pull request #190 from EasonLiao/snapshot

Let user decides when to take snapshot