Clean up and document the roadmap script

[jonschz]

• Add tests
• Improve the documentation of the arguments
• Add example calls to the README

Some comments:

First off: it must be said that this script is a little rough, and you could argue that it lacks a clear purpose. My reason for creating it was to identify smartheap functions in ISLE (see library_smartheap.h). It was helpful to see where there was a gap between known functions. The main asmcmp script doesn't show everything.

The --order feature came after. It makes an educated guess about how to order the modules in the makefile. For a given module, MSVC will put certain functions a long way from its neighbors. We try to remove the outliers to get the best average of where the module's contents should sit. You can compute this estimate for things other than functions, too. For example, vtables: --order VTA. AFAIK we haven't applied this information to LEGO1 but since we are coming to the end of new functions, maybe now is the time.

As far as tests: aside from one to just make sure it runs, maybe we could add some around the display features? For example: there is a bug in get_cmakefiles_prefix since I am now using ninja to build and the slashes go the other way. I think we could use pathlib to normalize this.

On line 244: print(prefix). I forget why this is there and it can probably be taken out.

Originally posted by @disinvite in #30 (comment)