luaengine: add memory-reading capabilities

[lucab]

This commit maps some more classes (device_t and address_space)
to retrieve devices and address spaces out of current running
machine.
Proxy methods are provided to enumerate/access devices and
address spaces, and to read memory content.

The idea is to provide user scripts some means to introspect on
current machine status.

Signed-off-by: Luca Bruno lucab@debian.org

[lucab]

This is v2 of my previous PR #72, taking into account @galibert comments.

Major changes:

• use luabridge instead of custom type, more C++ friendly
• map device_t and address_space to lua
• provide objects (userdata) for devices and address spaces
• expose .devices and .spaces property tables to enumerate available devices/spaces
• split previous single mem_read() into multiple read_<sign><size> methods

[lucab]

API usage is now as follow:

> for i,v in pairs(manager:machine().devices) do print(i) end;
:fatfury2_prot
:spritegen
:memcard
:banked_cart
:mslugx_prot
:maincpu
:screen
:kof2002_prot
:lspeaker
:saveram
:pvc_prot
:upd4990a
:ymsnd
:sbp_prot
:kof98_prot
:sma_prot
:audiocpu
:cmc_prot
:bootleg_prot
:pcm2_prot
:palette
:rspeaker
> for i,v in pairs(manager:machine().devices[":maincpu"].spaces) do print(i) end;
program
> print(manager:machine().devices[":maincpu"].spaces["program"]:read_i16(0xC1871C))
20085