* Switch to library requirements instead of source. As source puts extra source in install targets.
* Add top-level build for consistency and testing.
* Add support for root-less modular build/install.
* Add requires-b2 check to top-level build file.
* Bump B2 require to 5.2
* Increment b2 version require.
* Move inter-lib dependencies to a project variable and into the build targets.
