Changed util.py to __matrix_functions.py

This adds the __ notation to make the module "private". Tests have been
updated to import the functions from pymind instead of directly from
util.
Changed __matrix_functions.py to matrixfunc.py and created util.py

Moved initRandParams to util.py for organizational purposes. Also
renamed __matrix_functions.py to matrixfunc.py to make it clearer
where the matrix functions are stored so importing is clearer.
Added underscores to nnetwork.py and nnlayer.py

This clarifies that these modules are "private". Importing
pymind.components imports the classes that each module represents, so
retrieving these classes are as simple as importing pymind.components.
Updated nnetwork so that setWeights is placed in test file.