CompositeException

- reverting to version that just does printStackTrace
- see https://github.com/ReactiveX/RxJava/issues/1405
printStackTrace and getCause implementation

The printStackTrace and getCause implementations have different approaches to handling circular references.
If on a JVM where printStackTrace is called directly, the full causal chain will always be printed. If on one such as Dalvik
where getCause is invoked directly then it will cut the causal chain if it sees a duplicate.
Merge pull request #1632 from benjchristensen/composite-exception

Composite Exception - Circular Reference Handling
[Gradle Release Plugin] - pre tag commit:  '0.20.1'.
[Gradle Release Plugin] - new version commit:  '0.20.2-SNAPSHOT'.
0.20.1
Javadoc enhancements for new CompositeException implementation (mostly formatting).
Optimize single BlockingObservable operations

Backport from 1.x to 0.20.x of #1635
Merge pull request #1637 from benjchristensen/backport-blockingobservable-single-to-0_20

Optimize single BlockingObservable operations
[Gradle Release Plugin] - pre tag commit:  '0.20.2'.
[Gradle Release Plugin] - new version commit:  '0.20.3-SNAPSHOT'.
0.20.2
RxScala: Fix recursive onStart call in Subscriber
Deprecate ParallelMerge

Removing in 1.0 as it is confusing and rarely useful.
Merge pull request #1646 from benjchristensen/deprecate-parallel-merge

Deprecate ParallelMerge
Merge pull request #1641 from jbripley/rxscala-onstart-recursive

RxScala: Fix infinite recursive onStart call in Subscriber
Operator Scan Backpressure Fix

Problem 1) The initial value was being emitted before subscription which caused issues with request/producer state, particularly if filter() was used to skip that initial value and then called request(1) before the real request had been sent.
Problem 2) The initial value was not accounted for by the request so it was sending 1 more value than requested. It now modifies the request to account for it.
Problem 3) Redo relied upon these nuances to work. I've fixed this by using a simpler implementation that just maintains state within a map function.
Fix that Subscriber.onStart isn't called
Merge pull request #1651 from zsxwing/rxscala-onstart

RxScala: Fix the problem that Subscriber.onStart isn't called
Update RxSwing use of Scan

The initial value is sent when first onNext is sent, not at subscription time.