Enable using the git version of boost instead of an archive

[olicht]

Hi,

It would be great if I would be able to use the cloned version of boost instead of using an archive.
It would also allow to build new versions of boost much faster and check that they are not failing to compile.

By the why, excellent project!

[olicht]

@Orphis

[Orphis]

It's a bit complicated since the file layout is different from the merged archive actually.
The various macros defining the libraries and tests should have a bit of logic in there to make it work I guess, and then update all the libraries to handle that.

[Orphis]

I made #75 for this scenario.
It's not great though, listing all the modules could be done better, or maybe using a static list of per module dependency to add the right include directories for each lib only. To be refined later!