Let's try `date.jump( Day, -1 )`
Let's try `date.jump( Day, -1 )`

We can get rid of all the `deltaDay`, `deltaWeek` etc methods now.

Debatable whether it's worth getting rid of `nextDay()` etc also.

0b1kn00b/thx.core,andywhite37/thx.core,ciscoheat/thx.core,fponticelli/thx.core,mlms13/thx.core