[mesecons] Add NOR and OR gates, and documentation

mods/mesecons/mesecons_extrawires/doc/corner/description.html

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+Insulated corners are conductors that only conduct between the inputs (also not up or down). When placing they always point to the left in direction of your vision.

mods/mesecons/mesecons_extrawires/doc/crossing/description.html

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+Insulated crossing are conductors that conduct two signals between the opposing sides, the signals are insulated to each other.

mods/mesecons/mesecons_extrawires/doc/mese/description.html

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+The basic prerequesite for mesecons, can be crafted into wires and other stuff. Have a look at the <a href="http://wiki.minetest.net/Mese">Minetest Wiki</a> for more information. Mese is a conductor. It conducts in all six directions: Up/Down/Left/Right/Forward/Backward

mods/mesecons/mesecons_extrawires/doc/tjunction/description.html

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+Insulated T-Junctions are conductors that only conduct between the inputs (also not up or down).

mods/mesecons/mesecons_extrawires/doc/vertical/description.html

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+Vertical Mesecons only conduct up and down. Plates appear at the ends, at that place they also conduct to the side.