Added 2.6.0 Release Notes
Fixed formatting (fixup)
Removed redundant issue tags (fixup)
Added Sasha's updates (fixup)
Updated and rearranged.
Change to make Bug Fixes like the earlier versions
fixed typo
Merge branch 'release/2.6.0' into feature/2.6.0-release-notes
Add ref to FileSets docs so they can be linked; added link to release notes; fixed links in release notes.
Added release note about upgrading cluster and loss of messages (CDAP-745)
Merge branch 'release/2.6.0' into feature/2.6.0-release-notes

Conflicts:
	cdap-docs/reference-manual/source/release-notes.rst
Added MAVEN OPTIONs to the test commands.
Revert "Added MAVEN OPTIONs to the test commands."

This reverts commit 92580455086bfa4e9543182c4c63158eb2b08cd9.
CDAP-875 update cluster metrics reporter to handle the case when
the resourcemanager is run in HA mode.
CDAP-460: Updated docs to use new configurer style API for MapReduce
Removed link to earlier issues in Known Issues for 2.6.0.
fix upgrade queue tables
Updated known issue.
Fixed release notes. Fixed a broken cross-reference link.
Merge pull request #786 from caskdata/feature/program-api-change-docs

CDAP-460: Updated docs to use new configurer style API for MapReduce