Exceptions

* fix regression inserted with 8cba1a31
* [DoT] raise exceptions instead of printing errors
* improve test coverage

See merge request bortzmeyer/homer!25

Do not print error, instead raise an exception that need to be caught.
The calling method will then decide if the error should be displayed or
not.

Fix regression inserted with 8cba1a31

Readme, explain the goal of the tool.

See merge request bortzmeyer/homer!24

Partition code into modules
Remove --sync option

See merge request bortzmeyer/homer!23

Use an underscore '_' in front of the function name.

All the options are now stored in an object.