Force pint quantities

[srosenbu]

In the examples, physical quantities are created with pint and then directly converted to base units. We should force pint quantities in the function parameters. So instead of

a = (2.*ureg.meter).to_base_units().magnitude

some_function(a)

all methods in the library should be callable like this

some_function(2.*ureg.meter)

and the conversion to base units (or another compatible unit system) should be done by the code