This addresses multiple issues:
* Issue #63: initrd is build fresh each time, so tracked files do not matter.
* Issue #144: build time configuration
* Issue #123: allows us to customize the startup experience
* Issue #122: manual start-xen will go away
* Issue #25: tpmtotp PCRs are updated after reading the secret
* Issue #16: insmod now meaures modules
This adds compilations modules for musl-libc and kernel-headers.
The entire initrd (busybox, cryptsetup, gpgv, kexec, etc) can be built
with the much smaller libc and it appears to work with chroot.
Library paths are not set correctly and files are installed into
heads/install to make them accessible to other modules. This prevents
the initrd from working without manual fixup; need to fix before
merging into master.
Build times have gone up since everything is being rebuilt more
often for some reason.
