Input validation nn

[dktcoding]

Same deal as in the Matrix class, but with some comments this time:

• Added enable assertions in ant test
• There's no way of testing assertion failures in JUnit
• I'm not entirely sure you'll lilke 7f1d38a2b321d413dc869e2a8026d0d0cf285517

[dktcoding]

Horrible mistake, will fix later (found a lot of failing asserts)