mili: add Mili 15.1 project
This project downloads the Mili 15.1 library source code, extracts it, applies a few patches needed to the configuration and source code, and builds it. The build is a little unusual in that the Makefile generated by the configure step is within a subdirectory. Hence, the build and install steps are added by separate calls to superbuild_project_add_step. Furthermore, the install command is broken in the project's Makefile, so we install libraries and headers manually instead.