Browsing Activity Tracker

This extension provides a flexible way to log your browsing activity. In
particular, it allows you to track how much time you spend on websites. The
approach is minimalistic and give you direct access to the raw browsing data
that you can then analyze and aggregate to your taste.

In contrast, other extensions with the same purpose often require that you
create an account on their website and store your browsing data. Furthermore,
they only give you access to an automatically generated report with very little
control over how it is produced.

The extension notifies a callback URL by sending an HTTP POST request whenever
one the following events occur:

* a browser window is activated (gains focus)
* a tab is activated
* a webpage is loaded (when you follow a link, or navigate through your
  history)
* a browser window is deactivated (loses focus)

The body of the POST request is a JSON object containing the following keys:

* ``title``  Title of the webpage (typically the content of the ``<title>`` tag)
* ``url``  URL of the webpage
* ``time``  Time at which the event occurred. Number of milliseconds elapsed since 1 January 1970 00:00:00 UTC
* ``key``  A key identifying the browser sending the request
* ``favicon``  The URL of the webpage's favicon (or ``null`` when there is no favicon)

For window deactivation events, all the keys except for the ``time`` key are
set to ``null``.