add publish-m2 task for publishing to ~/.m2/repository.  Fixes #485.
API for evaluating a setting or task in multiple scopes
Docs: disable publishing for a project by overriding publishLocal to do nothing instead of deliver
docs: drop section in getting started on sharing settings

with vals allowed in .sbt files, it is not necessary to include it
Docs: present the TaskInputs page as motivation and for deeper understanding
Docs: cleaned up Tasks pages: clarified its purpose and reorganized
Docs: add section on getting values from multiple scopes
Correct data constructor for CrossVersion.binaryMapping. Fixes #716.
Docs: list multi-scope selection on changes page