NFD

Release ndn-cxx, NFD, version 0.5.1; ndn-tools version 0.4

• write release notes, update docs/release-notes-latest.rst symlink, add entry in docs/releases.rst
• update version number in wscript
• publish source and binary packages
• update documentation on named-data.net (generate documentation for the released version, update symlinks to "current", update version in github hook)
• send announcement