Syntax:
>> xyimagesc(X,Y,C)
>> xyimagesc(X,Y,C,...)
>> xyimagesc(X,Y,C,... 'PropertyName', PropertyValue ... )
The imagesc function works well when the user does not want the interpolation behavior of other functions. However if the data is not on an evenly spaced grid imagesc does not work.

This is not a very common situation but it may arise if the user wants to display something like a covariance matrix for a series of irregularly spaced measurements, which is why this function was written.

Notes:
- NaN values are displayed as white patches.
- all axis and figure properties should work when passed in as <'PropertyName', PropertyValue> pairs.