copy avm.sty to pwd during hlds to latex conversion

[arne-cl]

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