add docs for fileset and its example
addressed PR comments; also added an example for specifying an additional property for the output format
(CDAP-749) Make ProgramController Listener callback call sequence more predictable.
fix literal includes
remove app-manager scripts
(CDAP-749) Make Program TwillRunnable not to exit with failure
address comments; removed the use of Avro for explaining output format properties and used TextOutputFormat.SEPERATOR instead to be consistent with the FileSetExample
added more prose about input/output format and links to their javadoc
addressing jj's last comment
CDAP-821 Improve CLI error messages
Merge branch 'release/2.6.0' into feature/fileset-doc
Merge branch 'feature/fileset-doc' into release/2.6.0
Merge pull request #749 from caskdata/feature/fix-infinite-restart

(CDAP-749) Fix program infinite restart
Improve log messages and comments.
Merge pull request #757 from caskdata/feature/fix-error-message

Improve log messages and comments.
CDAP-838 Twill runnables should exit when any of the chained services complete
Merge pull request #756 from caskdata/feature/cdap-838_tx-abort

CDAP-838 Twill runnables should exit when any of the chained services complete
Merge pull request #754 from caskdata/feature/CDAP-821-cli-error-message

CDAP-821 Improve CLI error messages
fixup
Merge branch 'release/2.6.0' of github.com:caskdata/cdap into feature/cli-start-runtimeargs