Support for linker scripts

[davidlattimore]

Wild currently supports the bare minimum of linker script syntax needed in order to handle loading shared objects that are actually small linker scripts that say to load some other shared object, possibly with additional linker flags.

What it doesn't support is a user-provided linker script that specifies the layout of the file we're creating.

It'd be interesting to see how much of the linker script syntax and functionality we can support without killing performance.

Issue #36 needs to be done first though.