Issue #2560783 by stefan.r, joelpittet, lauriii, Cottser, Sutharsan, kgoel, justAChris, Gábor Hojtsy, dawehner, jhodgdon, effulgentsia, xjm, andypost, googletorp: Replace !placeholder with :placeholder for URLs in hook_help() implementations

Issue #2429617 by Wim Leers, Fabianx, Berdir, yched, dawehner, effulgentsia, catch, borisson_, jhodgdon, martin107, torgosPizza: Make D8 2x as fast: Dynamic Page Cache: context-dependent page caching (for *all* users!)