libvaladoc-dev software package provides API documentation generator for vala (devel files), you can install in your Ubuntu 14.04 LTS (Trusty Tahr) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install libvaladoc-dev
libvaladoc-dev is installed in your system.
Make ensure the libvaladoc-dev package were installed using the commands given below,
$ sudo dpkg-query -l | grep libvaladoc-dev *
You will get with libvaladoc-dev package name, version, architecture and description in a table
| Distro | Ubuntu 14 04 lts trusty tahr |
| Section | Library development |
| Package | libvaladoc-dev |
| Version | 0.3.2~git20140116-2 |
| Description | API documentation generator for vala (devel files) |
| Sub Section | libdevel |