+ Added map scale toggle for the ruler tool.
* Fixed possible conflicting measurements with different defined values

Here is a full disclosure of conversion_types units being used to calculate for each mode:
["u"] = 1 / 0.75,
["in"] = 1,
["mm"] = 25.4,
["cm"] = 2.54,
["dm"] = 0.254,
["m"] = 0.0254,
["km"] = 0.0000254,
["ft"] = 1 / 12,
["yd"] = 1 / 36,
["mi"] = 1 / 63360,
["nmi"] = 127 / 9260000,

if map scale is enabled

scale = 1 / 0.75

else

scale = 1

end

The final calculation of the function toUnit is:

result = (input_value * scale) * conversion_type

please tell me if any of these need to be corrected as I'm pretty sure they are based on wiremods.

Please be considerate and thankful. I do still read your comments.

Fixed more spelling mistakes
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