Zero plane displacement clamp in BMI

[hellkite500]

Related to #52 and #54 , when running the BMI model, we can try to prevent divide by zero conditions by clamping the zero plane displacement height.

Additions

• Validate that measurement height is >= zero plane displacement height in user provided config
• Ensure that zero plane displacement is > 0 by setting it to 0.01 (1 mm) if it is 0 or less
• Ensure that zero plane displacement is < measurement height by setting it to measurement height - 0.01 when they are equal. This ensure valid computations of the profile at nearly the measurement height.

Changes

• Config returns BMI_FAILURE and prints an error when measurement_height < displacement height

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[aaraney]

Logic looks solid, just a minor unit issue!

[hellkite500]

After a separate but related discussion with @ajkhattak I'm going to relax the validation/error conditions on wind speed displacement height < measurement height. There are some deeper assumptions in the pet code that handle this in non-obvious ways, but allow this condition to be "valid" still I think.

[hellkite500]

Changes to #54 ensure that the pet module can gracefully handle displacement and measurement height relationships in a meaningful way, so we don't need to handle that in BMI config parsing, but the displacement <= 0 is still reasonable to adjust here, I think.