Add vendored FlameGraph submodule and mk_flamegraph script for Linux.

[submodule "vendor/unity"]

	path = vendor/unity

	url = https://github.com/ThrowTheSwitch/Unity.git

[submodule "vendor/FlameGraph"]

	path = vendor/FlameGraph

	url = git@github.com:brendangregg/FlameGraph.git

#!/bin/sh

##################################################

# Construct a flame graph for a specific command.

# Linux-specific, and requires the "perf" package.

##################################################

CMD="$*"

if [ -z ${CMD} ]; then

    echo Usage: mk_flamegraph COMMAND

else

    # -g: call graph

    sudo perf record --freq=993 --all-cpus -g --output=perf.out -- ${CMD}

    sudo perf script --input=perf.out | vendor/FlameGraph/stackcollapse-perf.pl > out.perf-folded

    vendor/FlameGraph/flamegraph.pl out.perf-folded > perf_out.svg

fi

Subproject commit e8c88c24e9442ab18ee9d25083773e4f846b7bce