[SPARK-1981] updated streaming-kinesis.md

fixed markup, separated out sections more-clearly, more thorough explanations

Author: Chris Fregly <chris@fregly.com>

Closes #1757 from cfregly/master and squashes the following commits:

9b1c71a [Chris Fregly] better explained why spark checkpoints are disabled in the example (due to no stateful operations being used)
0f37061 [Chris Fregly] SPARK-1981:  (Kinesis streaming support) updated streaming-kinesis.md
862df67 [Chris Fregly] Merge remote-tracking branch 'upstream/master'
8e1ae2e [Chris Fregly] Merge remote-tracking branch 'upstream/master'
4774581 [Chris Fregly] updated docs, renamed retry to retryRandom to be more clear, removed retries around store() method
0393795 [Chris Fregly] moved Kinesis examples out of examples/ and back into extras/kinesis-asl
691a6be [Chris Fregly] fixed tests and formatting, fixed a bug with JavaKinesisWordCount during union of streams
0e1c67b [Chris Fregly] Merge remote-tracking branch 'upstream/master'
74e5c7c [Chris Fregly] updated per TD's feedback.  simplified examples, updated docs
e33cbeb [Chris Fregly] Merge remote-tracking branch 'upstream/master'
bf614e9 [Chris Fregly] per matei's feedback:  moved the kinesis examples into the examples/ dir
d17ca6d [Chris Fregly] per TD's feedback:  updated docs, simplified the KinesisUtils api
912640c [Chris Fregly] changed the foundKinesis class to be a publically-avail class
db3eefd [Chris Fregly] Merge remote-tracking branch 'upstream/master'
21de67f [Chris Fregly] Merge remote-tracking branch 'upstream/master'
6c39561 [Chris Fregly] parameterized the versions of the aws java sdk and kinesis client
338997e [Chris Fregly] improve build docs for kinesis
828f8ae [Chris Fregly] more cleanup
e7c8978 [Chris Fregly] Merge remote-tracking branch 'upstream/master'
cd68c0d [Chris Fregly] fixed typos and backward compatibility
d18e680 [Chris Fregly] Merge remote-tracking branch 'upstream/master'
b3b0ff1 [Chris Fregly] [SPARK-1981] Add AWS Kinesis streaming support
[HOTFIX][STREAMING] Allow the JVM/Netty to decide which port to bind to in Flume Polling Tests.

Author: Hari Shreedharan <harishreedharan@gmail.com>

Closes #1820 from harishreedharan/use-free-ports and squashes the following commits:

b939067 [Hari Shreedharan] Remove unused import.
67856a8 [Hari Shreedharan] Remove findFreePort.
0ea51d1 [Hari Shreedharan] Make some changes to getPort to use map on the serverOpt.
1fb0283 [Hari Shreedharan] Merge branch 'master' of https://github.com/apache/spark into use-free-ports
b351651 [Hari Shreedharan] Allow Netty to choose port, and query it to decide the port to bind to. Leaving findFreePort as is, if other tests want to use it at some point.
e6c9620 [Hari Shreedharan] Making sure the second sink uses the correct port.
11c340d [Hari Shreedharan] Add info about race condition to scaladoc.
e89d135 [Hari Shreedharan] Adding Scaladoc.
6013bb0 [Hari Shreedharan] [STREAMING] Find free ports to use before attempting to create Flume Sink in Flume Polling Suite