Compiling via cmake with MSVC

Modified cmake scripts and added the finder module for pthread and mkl.
One modification in the source to successfully compile.
instead of doing this, can you kindly try:

```cmake
PREFIX "_"
```

and then in `convnet.py` change the `lib_name` to:

```python
lib_name = "_convnet"
```

Finally in `include/pyconvnet.cuh` the `extern "C" PyMODINIT_FUNC initconvnet();` becomes:

```c
extern "C" PyMODINIT_FUNC init_convnet();
```

and the same in `src/pyconvnet.cu`:

```c
PyMODINIT_FUNC
init_convnet() {
    (void) Py_InitModule("_convnet", _ConvNetMethods);
    ...
```