Battery simulator process eats all the memory and causes the machine to crash.

[cassman42]

When running the battery simulator it caused the Pi to crash. Having eaten all of the memory and caused various things to die!

My data goes from May 2016 - hence the process starts 31,449,986 data points behind!

I've looked at the code and added a new method in common.php, this will cause the existing buffered data to be written out
and the buffer cleared - so that it doesn't consume all the memory - it also makes the process significantly faster.

[cassman42]

I've raised a PR

#23