build: use wrapper script to run drumfish in src dir

Use a wrapper script so that we can setup our LD_LIBRARY_PATH and any
future variables we need to set when running drumfish from within the
source directory. This is a poor mans libtool wrapper script.
build: bring simavr in as a git submodule

Brought simavr in as a git submodule so you don't have to build and
install it before building drumfish. Its currently pegged to my merged
branch which includes fixes for drumfish and potentially extra features
and will always be merged and not rebased going forward.