Add support for reading and writing to I2C devices from lua

[rosaage]

This is essentially just a wrapper for the exisiting C functions.
Writing is currently set to require PERM_MEMORY

I have tested this a bit, and it seems to work ok
The syntax is i2c.read(device_id, register, length) and i2c.write(device_id, register, data_table)
Reading returns a table of values, while writing returns a bool True on success or errors on a fail.
(Should this return a false and a string instead of error?)

Test script

print("Hello World!")

print(CONSOLE_TYPE)

-- device 3 is the mcu
-- 0x09 is volume slider
ui.echo(i2c.read(3, 0x09, 1)[1])

-- 0x0D is the system voltage
local volt = i2c.read(3, 0x0D, 1)
local voltf = volt[1] * 5 / 256.0
ui.echo(voltf)

-- 0x28 is Brightness of the WiFi/Power LED 
ui.echo("Reg: "..i2c.read(3, 0x28, 1)[1])
i2c.write(3, 0x28, {200})
ui.echo("Reg: "..i2c.read(3, 0x28, 1)[1])
i2c.write(3, 0x28, {150})
ui.echo("Reg: "..i2c.read(3, 0x28, 1)[1])
i2c.write(3, 0x28, {70})
ui.echo("Reg: "..i2c.read(3, 0x28, 1)[1])

-- 0x15-17 is not in use
local data = i2c.read(3, 0x15, 3)
ui.echo(string.format("Reg: %d, %d, %d", data[1], data[2], data[3]))
i2c.write(3, 0x15, {20, 30, 40})
data = i2c.read(3, 0x15, 3)
ui.echo(string.format("Reg: %d, %d, %d", data[1], data[2], data[3]))

Volume slider reads fine, voltage reads back 3.68 (seems ok), I don't see any LED stuff, but when reading back the same register I see the changes. The final test is reading and writing multiple registers, this also seems to work ok.

[ihaveamac]

while writing returns a bool True on success or errors on a fail.

In this case I think it should not return anything, and raise an error if it fails. Or if there is a reason to return a specific value, then return that.

[MisterSheeple]

Since malicious or negligent i2c writes have the potential to cause bricks, I think an unlock mechanism that makes the user aware that the script is about to write to i2c would be pretty important to have.

[rosaage]

Writing now returns nothing (nil) on a success or lua error on fail