Add volumetric limit to tune menu

[vovodroid]

This allows more handy speed limit editing in real time.

[vovodroid]

May be float31? 12.3 good enough.

[vovodroid]

By a way, for what it's worth, float specifiers, including float_42_52 produce precision errors, resulting in inability to set zero value:

In this case it sets limit to 0.001 instead of disabling it, actually ruining the print.

[thinkyhead]

In general rational numbers don't make for the most perfectly rounded float values, but I'll look closer at unscaleEncoder to see how it can perform more perfect rounding to the specified 100ths precision.