docs: add "spray-M8-released" blog post, smaller improvements
site: small fix for blog URIs
site: tweak logging levels
sbt; remove ls-sbt
docs & site: update for 1.0-M8.1, smaller fixes
routing: add headerValueByName(Symbol) and optionalHeaderValueByName(Symbol) overload
docs: restructure Project Info chapters, add "External Resources" chapter, closes #250, #192
docs: restructure Introduction chapters, add getting-started, closes #74
doc start
CORS headers model and parser

First part of support for CORS
Revert "doc start"

This reverts commit 9cdab2ab7b67bb8db8f25b5b39f8b1e21824f5d7.