luaengine: add memory-reading capabilities

These commits add a new LUA namespace and a method to
read data from the main address-space.
The idea is to provide user scripts some means to introspect on
current machine status, eg. to programatically draw a HUD.

Signed-off-by: Luca Bruno <lucab@debian.org>

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To ease development on my side, this branch is depending/embedding PR #71. It is ONLY up for review at this point. I will rebase on master as soon as the other one gets merged.