Add changelog for 0.18.0.
Bump version to 0.18.0.

Changes:

* Do not set a default value for the vendor attribute.
  WARNING: This changes the default package names!
* Change package name computation regarding version, revision and vendor.
  WARNING: This changes the default package names!
* Start default revision at 1.
* Unbreak omnibus packaging. (#64)
* Add support for npm recipes. (bracki / #65)