Mark std.range.cycle for static array and their unittests as system
Use version-specific navbar when building docs.
Use -prerelease for navbar ddoc instead of hardcoded version.
add upgrade hints
Merge pull request #2777 from WalterBright/upgrade

add upgrade hints
Merge pull request #2769 from tom-tan/system-range-cycle-for-sarray

Mark std.range.cycle for static array and their unittests as system
Merge pull request #2774 from quickfur/versioned_navbar

Use version-specific navbar when building docs.