Improve Timer Thread Usage

[amarqueslee]

I have already offered some work to improve our use of timers in this plugin as part of issue #17 . @yuttie has kindly suggested some additional changes which I agree would offer further improvement.

His relevant notes from the referenced issue:

We need to improve the other change for another issue of this plugin.
Thanks to your patch, I found that my original code redundantly starts a new tick thread whenever comfortable_motion#flick() is called, which causes unnatural acceleration.
The second change actually fixes the problem by maintaining only a single persistent tick thread.
However, it also introduces constant CPU usage even when a user doesn't use a vim.
I think we can improve the patch by stopping a tick thread when it is not needed.
This problem should be discussed in another issue.

My initial idea of how to approach this is to retain a single script-wide reference to a tick thread (represented by a timer ID), initially not started. If comfortable_motion#flick() is called when the thread is stopped, we will start the thread (call timer_start). If comfortable_motion#tick() is called and it discovers that scrolling has stopped, it will stop the thread with timer_stop.

@yuttie, does this approach seem appropriate to you?

[yuttie]

I merged #23 , and now I think this issue is resolved.
Closing.