modularization refactoring

Today we discussed with @zainsohail04 and @kutnyakhov that the idea of splitting all the functionalities of sed in different packages might not be viable at the moment. This is simply due to the amount of overhead work needed to maintain these packages (multiple repeated packaging and environment tools, changes in one package requiring manually updating versions in others, etc..), which distracts from developing the important features we want to work on.

In this pull request I suggest a change to the structure of this package which makes it more modular. This way we will keep the same separation structure we discussed, but all in a single package, which we should rename sed-processor.

I suggest this as a starting point, and if in the future we have the feeling one of the sub-modules in this package should have a life of its own, we can easily detach it.

I do not want to impose this, and therefore I ask for the approval of everyone to make these changes permanent. If someone disagrees, with a valid argument, then I will delete this and proceed with the separated packages approach we had previously discussed.