Add performance tests

test/perf contains performance tests

perf.jl runs a sine wave Kalman filter in Julia
perf.py runs the same sine wave using PyKalman
perf.sh runs both of the two implementations, times them, and saves
the data to benchmarks
Remove pylab from import statements
Fix paths in perf.sh
Fix paths in perf.sh again
Make sure root has a Kalman.jl copy
Fix typo
Remove Pkg.update directives
Change benchmarks header