Move `should` related stuff to separate page & update docs to use `expect`

The rate at which I am updating documentation, soon there will be no documentation of `should` at all.

I think it would a good idea to move should related documentation into its own page along with an explanation as to why the shift from `should`  syntax to `expect`.

So this way as long as `should` syntax is supported we atleast have docs that explain their usage. The day `should` is deprecated we can remove the page too.