Do not ignore empty topics
Extract XHTML-IM inline imags by default

- Add two new options: tmp_image_dir and extract_inline_images
- tmp_image_dir is $XDG_CACHE_HOME(usually ~/.cache)/poezio/images if unset
- Name the images from a SHA-1 of their data and their mimetype
- Output file:// links inside the message
Document the group_corrections option
Keep the default config options in a dict and make the “default” parameter of config.get() optional

the Config object now also optionally takes a dict of default values
in its constructor.
Change the API of Config.get_by_tabname

Make the "default" parameter optional and thus move it to the end of
the command with the other optional parameters.

And change all the calls.
Remove the (sometimes wrong) default values in the config.get() calls
If the whitespace_interval value set in the config is null or negative, don’t send any
Make the runtime changes to max_lines_in_memory useful
Initialize PluginConfig properly
Fix #2713 (make /set <option> return the value of the option)

Should work for any case (plugin, different section, etc)
Fix #2719 (write/read in the plugin config files even when not loaded)
Typo
Make the features disco in chat more user-friendly
Use a setuptools entry point instead of a custom script
Prevent a (harmless) traceback while generating the documentation
Mention that setuptools is kind of mandatory
Add some unit tests using py.test

- we need to have more
Fix the requirements.txt (don’t install potr in editable mode)
Add a .travis.yml file for travis-ci
Fix the dependencies in the setup.py