Prepares AddFile for major refactoring
Removes posts and templates paths from Generator
Makes template changes handle relative paths
Makes post changes handle relative paths
Adds asset handler interface
Creates template handler
Creates post handler
Creates generated content handler
Creates markdown page handler
Creates transformable content handler
Creates static content handler
Moves posts logic to post handler
Simplifies post handler dependencies
Moves templates logic to template handler
Simplifies generated content handler dependencies
Simplifies markdown page handler's dependencies
Simplifies remaining handlers dependencies
Removes Generator dependency from Handlers Manager
Run command no longer uses Generator

It still references Generator, though, because of watch command.
Creates common class for 'watch' and 'run' commands