[mongodb] update parameter for connection url to match previous behavior and docs.

Changes:
1. mongodb configuration parameter bug (mongodb.url)
2. README file change
3. Some cleanup. Default DB is 'ycsb'

closes #302 ycsb launcher should only include binding specific jars in the classpath

the classpath, rather than all of them.

As a part of branching to stage 0.2.0 release in #266, set version
for continued development on master branch.

[voldemort] disable voldemort pending maven accessible artifacts.

[packaging] ensure datastore binding specific distributions include core transitive deps

closes #279 

closes #297

classpath, rather than all of them.

Add build instructions to README, update DB-specific build docs.

[packaging] refactor packaging to avoid fat-jars.

* remove unused declared deps in a few places
* lex sort modules in top level pom
* update maven plugin versions.
* no more jar-with-dependencies
* set ycsb-core to provided in bindings
* introduce a bindings-parent pom that sets
** stage dependency copy on building binding
** iff binding has a README.md, build a binding-specific dist artifact
* update distribution assembly to
** properly build after modules
** use per-binding sets of dependencies

closes #250

    [core] use HdrHistogram and fix coordinated omission

also closes #10

- Make status interval configurable

- Output old histogram or HdrHistogram or both
- Potentially output HdrHistogram to log file on status interval.

Add a joined histogram measuremement to compare old/new histogram
outputs.

Add option for controlling the feature(default on).

Remove needless synchronization by using CHM in Measurements.

Add option to randomize delay(default=true, as before)

throttle method in client.

1. mongodb configuration parameter bug (mongodb.url)
2. README file change
3. Some cleanup. Default DB is 'ycsb'