We build all the tools into a single virt-mem executable, in order to
share the most runtime.  Almost all the code between individual tools
is shared anyway.

lib/

 - The common core of all the tools.  Library, kernel symbols, command
   line handling, memory images, etc.

   lib/virt_mem.ml contains most of the important code.

uname/
dmesg/
  etc.

 - The code specific to each tool, usually rather small.

mem/

 - This brings everything together and links it into a single executable.
   Other than that purpose, there is almost nothing in this directory.