Merge branch 'issue#4' into 'devel'

Issue#4: Collaborators, DESCRIPTION and REAMDE

This branch:
  - Put @walmes and @fernandomayer as collaborators;
  - Add sections to DESCRIPTION file;
  - Add `buildPkg.R` file to generate documentation, test, build, upload sources to public directory;
  - Add `README.{Rmd,md}` that contains small description and installation details for all OS.

See merge request !2