Add support for moves across root modules

[busser]

What remains to be done:

• Replace the internal/format package with a new pkg/pretty
• Replace the -show-analysis flag with a new -verbosity flag
• Get the -no-color flag working again, and add support for NO_COLOR
• Add tests to the new pkg/engine package
• Add tests to the new pkg/terraform package (especially the Write* functions)
• Add tests to the new pkg/pretty package
• Add end-to-end tests for the cross-module feature
• Add smoke tests to catch invalid configuration ASAP (eg: multiple modules + moved blocks)