change draw_chart to google_chart_tools_draw_chart to preserver namespace ()

Two methods for dealing with this in my mind:

google_chart_tools_draw_chart is the default but draw_chart also exists (which just calls google_chart_tools_draw_chart to maintain historical compliance)
draw_chart calls google_chart_tools_draw_chart but also sets a drupal message indicating that the function draw_chart is deprecated

My vote would be for option 2 as well as additions to the README, issue log, and maybe even an update hook that displays the same message. I'm not sure how much usage you've seen by developers off of this module so not sure what's the best way of handling it but I'd probably support it but deprecated for the next release and then drop it the one after.

message only triggered if someone is still calling draw_chart. Draw chart would look like this

function draw_chart($settings) {
  drupal_set_message(t('A function called draw_chart(). Please update this function call to google_chart_tools_draw_chart().'), 'warning', FALSE);
  google_chart_tools_draw_chart($settings);
}

Yeah, I think it should only be in one or two releases. A bit goofy I agree but better then just outright dropping it.