script: create doc_utils.py module for commonly used methods

For now it only has "tabularize", a method extracted from
scripts/bitbake-metadata2doc.py that creates reST tables from
bi-dimensional lists.

Also, the method is slightly different from the original, as it applies
rstrip() to the generated table header and rows to avoid polluting the
commit diffs with blank spaces.

Signed-off-by: Lucas Dutra Nunes <ldnunes@ossystems.com.br>
Ignore compiled Python files

Signed-off-by: Lucas Dutra Nunes <ldnunes@ossystems.com.br>
scripts: add bugs tables generation script

This script is also called two times on bitbake-metada2doc.sh to
recreate the files open_bugs.inc and closed_bugs.inc.

Also, it uses the 'tabularize' method from doc_utils.py

Signed-off-by: Lucas Dutra Nunes <ldnunes@ossystems.com.br>