first minimal core of the package with tests

Signed-off-by: Luca Lianas <lucalianas@gmail.com>
improved errors handling

Signed-off-by: Luca Lianas <lucalianas@gmail.com>
handle database overwrite

Signed-off-by: Luca Lianas <lucalianas@gmail.com>
bugfix
renamed invalid URLs exception
minor refactory
database overwrite not allowed
added add\get\delete document methods (and tests)
switched to lxml
added a way to have a 'silent' logger (useful to developers)
added XPATH queries support
added pip requirements file
added TravisCI file
added TravisCI build status icon on README.md
added package doc
extended setup.py
fixes setup.py to properly generate PKG-INFO
fixed RST text
added MANIFEST template
ignore MANIFEST file (automatically generated using MANIFEST.in)