Add configurable delays for setting highlights and signs

Setting highlights and signs repeatedly can slow down editing in Vim slightly. It would be nice to be able to configure settings for delaying the placement of highlights and signs. Two new settings could be added for delaying either highlights or signs. When the numbers are above `0`, the existing functions for setting the highlights or signs could be called after a short delay. The timer would be reset each time new results come through for a buffer. This would make it so several quick edits to a file could be made faster.