Lock-free, MPSC-queue based, fast-path serializing Observer.
Update docs for "apply" and add an example
JMH Tests for Simple Use Cases
Remove Subscription Wrapper from Observable.subscribe

Performance increase from 7.7m to 8.8m ops/second

Before:

Benchmark                              (size)   Mode   Samples         Mean   Mean error    Units
r.u.PerfTransforms.mapTransformation        1  thrpt         5  7714453.187   362218.633    ops/s
r.u.PerfTransforms.mapTransformation        1  thrpt         5  7527144.767   497816.471    ops/s

After:

Benchmark                              (size)   Mode   Samples         Mean   Mean error    Units
r.u.PerfTransforms.mapTransformation        1  thrpt         5  8853534.333   183494.242    ops/s
r.u.PerfTransforms.mapTransformation        1  thrpt         5  8806958.403   452595.219    ops/s
Merge pull request #1243 from benjchristensen/perf

Remove Subscription Wrapper from Observable.subscribe
Observable.from(T) using Observable.just(T)

For code like `Observable.from(1)` Improve performance from ~3.9m to 4.5+m ops/second

Before;

```
r.u.PerfTransforms.flatMapTransformsUsingFrom        1  thrpt         5  3923845.687    46657.660    ops/s
r.u.PerfTransforms.flatMapTransformsUsingFrom     1024  thrpt         5     8924.953     1983.161    ops/s

r.u.PerfTransforms.flatMapTransformsUsingFrom        1  thrpt         5  3623228.857   490894.492    ops/s
r.u.PerfTransforms.flatMapTransformsUsingFrom     1024  thrpt         5     9176.330      923.929    ops/s
```

After:

```
Benchmark                                       (size)   Mode   Samples         Mean   Mean error    Units
r.u.PerfTransforms.flatMapTransformsUsingFrom        1  thrpt         5  4052364.587   100971.234    ops/s
r.u.PerfTransforms.flatMapTransformsUsingFrom     1024  thrpt         5    11682.783      496.656    ops/s

Benchmark                                       (size)   Mode   Samples         Mean   Mean error    Units
r.u.PerfTransforms.flatMapTransformsUsingFrom        1  thrpt         5  4700583.987    77742.037    ops/s
r.u.PerfTransforms.flatMapTransformsUsingFrom     1024  thrpt         5    12588.803       58.935    ops/s
```

Using this test:

```
../gradlew benchmarks '-Pjmh=-f 1 -tu s -bm thrpt -wi 5 -i 5 -r 5 -prof GC .*PerfTransforms.flatMapTransformsUsingFrom*'
```
Merge pull request #1244 from benjchristensen/from-just

Observable.from(T) using Observable.just(T)
Update README.md to new constructors
Moved to atomic field updaters.
Add zip(iterable, selector) to RxScala; resolve the issue of zipWithIndex; update CompletenessTest.scala
Fixed testConcurrentOnNextFailsValidation
Merge pull request #1239 from zsxwing/apply-scaladoc-example

Update docs for "apply" and add an example
Merge pull request #1248 from akarnokd/SchedulerTestConcurrentFix

Fixed testConcurrentOnNextFailsValidation
Rename to 'zipWith';  add 'zip(iterable)'; add examples
ZipIterable unsubscription fix.
Changed lazySet to regular volatile write to avoid potential visibility issues.
Make the chunk_test.clj work again for now
Fix the bug that BlockingObservable.singleOrDefault doesn't call unsubscribe
Merge pull request #1246 from akarnokd/AtomicReferencesToFieldUpdaters

Moved to atomic field updaters.
Merge pull request #1254 from akarnokd/ZipWithIterableFix

Merge pull request #1254