copy avm.sty to pwd during hlds to latex conversion

We can convert an HLDS XML file to an attribute-value matrix formatted with LaTeX and generate a PDF file from it. Right now, this only works if we're in `src/pypolibox` (since `avm.sty` has to be present).

```
hlds-converter -f latex pypolibox-tccg.tmp | pdflatex
```
