The feature is heavily laced with warnings and a complete lack of
promises around future compatibility. But within those parameters,
it might allow some people to do cool things.
Fixes#60.
iPXE appears to have *really* poor performance (orders of magnitude worse) if
it doesn't know the length of the kernel/initrds that it's downloading. Without
this change, booting CoreOS takes longer than I've had patience to wait. With
this change, the bottleneck becomes the network transfer speed.
Fixes#10.
This allows API servers to return URL(x) in the cmdline template,
which pixiecore translates to an appropriate ID(x) template call
to get the file proxied via Pixiecore.
The main difficulty in passing a commandline as a plain string is
that you sometimes want to encode IDs into it, to tell your kernel
to fetch something via Pixiecore. Solving that problem with maps is
a bit clunky. Instead, now we use a text/template {{ ID "foo" }} to
mean "make a URL that, when fetched, reads the file "foo" from the
Booter.
