init_xml that you found is ok.

For an action at installation time, you can also use "function" tag in any normal xml data file, thus calling a function from specified model, see example of "function" tag  in the answer here. 

For an action at uninstall time (as well as at install time) may work following workaround:

python [8.0 api]:

from openerp import models, fields, api
import logging
_logger = logging.getLogger(__name__)

class handle_install_uninstall(models.Model):
    _name = "handle.install.uninstall"

    name = fields.Char('Name')

    @api.model
    def create(self, vals):
        _logger.info("Installing...")
        # installation time code...
        # you can use self.env.cr or self._cr here...
        return super(handle_install_uninstall,self).create(vals)

    @api.multi
    def unlink(self):
        _logger.info('Uninstalling...")
        # uninstall time code...
        # you can use self.env.cr or self._cr here...
        return super(handle_install_uninstall,self).unlink()

XML:

<openerp>
    <data>
        <record id="handle_install_uninstall_rec" model="handle.install.uninstall">
            <field name="name">Install - uninstall handler</field>
        </record>
    </data>
</openerp>

add the above XML file in __openerp__.py manifest as normal 'data' xml file. then record of this model will be created at installation time (consequently "create" method is called and your code executed), when you uninstall module, then record created this way will be deleted at uninstall time, so if this deletion does not bypass the Odoo ORM, then "unlink" will be called and your uninstallation time code will be executed. please make sure that you do not create more then one record of this object in the same database in order to have your code called only once. I never tried this, but normally it should work. Probably there should be better way to call function at uninstallation time, but I do not know such.