BUMP 2.6.6
DOCS-4488: more tickets for the 2.6.6 release notes

Signed-off-by: Sam Kleinman <samk@10gen.com>
DOCS-4488: fix syntax for 2.6.6 release notes

Signed-off-by: Sam Kleinman <samk@10gen.com>
DOCS-3388: edits to release notes