Modularization of scripts

[JavierCoronel]

Hi, I found the repository after realizing BR charges for converting epubs... Thanks for the code, it works like a charm!

I worked a bit on the code to make it more modularized and readable. Also uses the fire module to simply use arguments from the console. I added a bit of refactoring for generating the bold text and it works now on specific tokens of the text. This will help for instance for special characters and word contractions like We're, I'm and so on