Fixes with Fred's test changes

1. Implemented a new public method to return XML fragment of "_raw"
field, which may have segmentation markers i.e. <sg> elements. Added
test code for it.
2. Changed test expected files for xml escaping and validation for the
method mentioned above.
3. Fixed a code regression from earlier code cleanup.
Note that one ATOM test (part of Fred's test suite) fails. It is for
Splunk version prior to 4.3., where 'Feed' element is missing from
Splunk server. We don't handle this in the SDK. I'll open a JIRA item
for tracking.
Turning off multi reader json test for 4.x Splunk

Multi JSON reader is only supported with 5 (or higher).
Changed for code review feedbacks

1.Readablity improvements, including method renames. Most is to give
more distinct names for readablity.
2. Use StringWriter rather than byte stream to avoid double charset
conversion.
3. Added code comments into ResultReader.cs to document class
relationships and code flow.
Readablity and supportability improvements

Includng code comments, renames and refactoring motivated by code review
feedbacks.
More code comment changes
Java doc and class access modifier changes

It is done for more specific method descriptions in Java docs and allow
application to call close on multi readers.
Doc related changes and code cleanup

1. Update CHANGELOG
2. Removed unnecessary type generics in ResultsReader
3. Indentatoin fix from David's feedback
4. Javadoc fixes from Intellij Analy
5. Rather than raising exceptions when no result sets are found after a single
   reader is constructored, just return nothing without failing. This is
   consistent with multi readers and is backward compatible.
Merge pull request #37 from splunk/feature/results_reader_t_fix

Fixes with Fred's test changes, and cleanup including readablity improvements motivated by code review feedbacks.