High CPU comsuption for style changes

[maple-leaf]

Machine Info:

  Model Name:	MacBook Pro
  Model Identifier:	MacBookPro15,1
  Processor Name:	Intel Core i7
  Processor Speed:	2.6 GHz
  Number of Processors:	1
  Total Number of Cores:	6
  L2 Cache (per Core):	256 KB
  L3 Cache:	12 MB
  Hyper-Threading Technology:	Enabled
  Memory:	16 GB

OS: macOS Mojave 10.14.6 (18G103)
Rust version: 1.45.1

Steps to reproduce:

1. Run 'todos' in examples of the repository
2. Create a todo item
3. Hover and un-hover a todo item quickly. This operation uses up to ~18% CPU.
4. Resize the window width quickly. This operation uses up to ~60% CPU. And sometimes it stops responding to resize.

https://www.loom.com/share/2b5d2151eec740c4a109656249335d13

[hecrj]

Thanks for the report! This is related to #241.

Style changes are not really the cause of the issue, but just the fact that we are currently redrawing all the time (i.e. on every mouse event). I have plans to tackle this relatively soon.