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.