Updated Velocity Version

The new version (1.7) provides some nifty features like foreach.
generate.groovy: Add support for map and list values in .list files.

This opens a wide variety of new possibilities in template files. Syntax
for maps and lists is similar to velocity syntax.
Example: {key:value,list:[a,b,c]}

This commit also changes splitting of value pairs from .list files.
Add test for new functionality in generate.groovy
Add .vm and .list for arithmetic interfaces
Add .vm and .list for RealType implementations of arithmetic interfaces

The variables meanings can be described as:

imports - list of additional imports, see .vm for already imported packages.
javadoc - main javadoc for generated class.
interface - arithmetic interface which is implemented by this op.
authors - list of authors which will be added as javadoc @author
compute_expr - (optional) if this is set, it will be used as the expression to
	set the output to: ```output.setReal(${compute_expr});```
compute_body - (optional) if this is set, the contents of this variable will
	be inserted into the compute method.
omit_return - (optional) set to anything to not add ```return output;``` at
	the end of the compute method. This may be used if this statement al-
	ready exists in the compute_body.
constructor - Additional code to add to the contructor of this op.
members - List of members, which are represented as a map of properties:
		name - member name
		type - member type (default: double)
		modifiers - string of modifiers, e.g. "static final". Private
			is allways prepended.
		init - statement to set this member to in the class body
		construct - statement to set this member to in the class
			constructor
	All properties except name are optional.
WORKAROUND: Increase priority of InvertII

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Add statistics test

Additional tests for min, max, mean and stddev ops.  The tests all follow the same pattern.

1.  Generate a random test image.
2.  Get a reference to the raw data pointer.
3.  Calculate the statistic by directly using the raw data.
4.  Calculate the statistic by calling the op.
5.  Assert that the two values are the same.
Add generateFloatArrayTestImg

Add a new function to make a floating point test image.  The image is populated with
random values.
MaxRealType, MinRealType: bug fixes

Changed MinRealType.java and MaxRealType.java test to use copies of the 'it.next()' container.
MeanRealType: bug fix

Mean was previously calculated as size/sum.  Changed to calculate sum/size.
Modify mean test

The mean test previously asserted that the mean of a random buffer was 15.625.  The mean
op was subsequently changed to return "sum/size" (previously the op had returned "size/sum").
Thus the test needed to be changed to assert that the mean of the buffer is 1/15.625.

An additional simple "sanity check" was also added that works as follows:

1.  Populate all pixels of an image with a constant value of 100.0.
2.  Calculate the mean using the op.
3.  Assert that the mean is equal to the constant value of 100.0.