HRDIC data loader not working for davis 10 files

[mikesmic]

Issues to fix for davis 10 format

• Coordinate values are formatted as floats (even for int values)
• Coordinate values are not necessarily integers (Only half integers because of odd sized integration windows?)
• Coordinate values can -ve
• Possibly different units for coordinates and displacements, assumed to be the same when calculating strain currently

[rhysgt]

In investigating this, I've realised that number in the DaVis header is not the sub-windows size but the step size. We should clarify this in the code. The effective shear strain maps compare reasonably well with the ones from DaVis, regardless of the chosen overlap. The effective shear strain maps from DefDAP look a lot sharper than the ones from DaVis.