Add convenience primitives

[kleinreact]

The PR adds some more high level primitives that are convenient to use during Clash circuit design. In particular, the PR adds:

• the static left and right shift operators (<<%) and (%>>)
• the apWhen apEn primitive, which is just a convenience extension of mux
• the regEnN primitive, which is the probably most primitive FIFO just chaining regEns.

Still TODO:

• Write a changelog entry (see changelog/README.md)
• Check copyright notices are up to date in edited files

[gergoerdi]

As a small comment, to me the name apWhen conjures the idea of whenA :: (Applicative f) => f Bool -> f () -> f (). I think your apWhen is more closely related to regEn, so maybe apEn or updateEn or something would be a more intuitive name?

[kleinreact]

As a small comment, to me the name apWhen conjures the idea of whenA :: (Applicative f) => f Bool -> f () -> f (). I think your apWhen is more closely related to regEn, so maybe apEn or updateEn or something would be a more intuitive name?

I totally agree. I'm happy with apEn as well. It's nice, short, free and appealing.

[martijnbastiaan]

As discussed on Slack:

• The shift primitives should be called %<<. and %>>. to fit the patterns set in Data.Bits
• The shift primitives should work on Bits a, as doing it on BitPack a leads to unexpected behavior for signed numbers.

We've decided to drop it from this PR.

[kleinreact]

I removed the static shift operations from the PR.