Pyxel's new palette
Now I'm considering a new palette for Pyxel.
Please give me feedback on it.

![pyxel-palette](https://user-images.githubusercontent.com/678802/72732939-36694780-3bda-11ea-9a8e-a14920b1307e.png)
![nog20200119b_sample拡大](https://user-images.githubusercontent.com/678802/72732943-39643800-3bda-11ea-9f3f-7e095884cecb.png)
![nog20200120a_8x8ACT拡大](https://user-images.githubusercontent.com/678802/72732951-3a956500-3bda-11ea-85c8-1436bb8ca95b.png)
![nog20200120c_8x8拡大](https://user-images.githubusercontent.com/678802/72732957-3bc69200-3bda-11ea-9dbd-79dc7b94df16.png)
