Lambda variable in softmax

[theshoonyam]

In softmax regression, lambda variable conflicts with that of lambda function in python bindings. Hence writing the code in python results to this output:

model = mlpack.softmax_regression(training=inputdata,labels=labels,number_of_classes=2,max_iterations=100,lambda=0.0001) File "<stdin>", line 1 model = mlpack.softmax_regression(training=inputdata,labels=labels,number_of_classes=2,max_iterations=100,lambda=0.0001) ^^^^^^ SyntaxError: invalid syntax

I have changed the variable name to lambdas to fix the same.

[rcurtin]

The parameter is automatically renamed lambda_ when the Python bindings are built and the documentation accordingly calls the parameter lambda_: https://www.mlpack.org/doc/stable/python_documentation.html#softmax_regression

See also #3302.