Performance improvement when transmitting

The 'checked' table is passed by reference anyway, so reassigning it at
every step along the network is just wasting time by creating more and
more copies of it.
Update deprecated api calls
Make lcd text persist properly
Use tabs instead of spaces, remove unnecessary spaces
Merge remote-tracking branch 'CiaranG/tableperf'
Use tabs instead of spaces and remove unnecessary return
Merge https://github.com/Jeija/minetest-mod-digilines

Conflicts:
	digilines/internal.lua
	digilines_lcd/init.lua
Replace chunk of unnecessary code with gmatch