[examples] Replace Jade with Pug

[notrab]

This fixes #3181

I've gone ahead and replaced all of the examples to use Pug instead of Jade.

[notrab]

Node 4+ would allow this to be written as

a(href=`/user/${user.id}`)= user.name

[notrab]

@dougwilson Would you be happy to merge this?

[dougwilson]

Hi @notrab this is awesome, thanks so much for putting this together!

[dougwilson]

I've been looking at pug and trying to figure out their Node.js version support. It seems like they broke support for Node.js 0.10 recently, and added it back, but only because of web browsers, not because they wanted to support Node.js 0.10. Their Travis CI config only tests on Node.js 4 & 6. It does seem like beta9 supports Node.js 0.10, so that's good, but all it's deps use ^ which means that we can turn around and can no longer build Express if this suddenly changes.

[notrab]

Excellent. I wasn't too sure on the dependency tree and Node support. I really wanted to use template literations and some ES6 syntax but I held back so there were no breaking changes in the examples alone.

I've seen a few issues regarding new up to date examples and I more than happy to provide a few but in cases like this, it might be better to pull out some examples into another repo, so those who wish to use newer versions of Node can use things like fat arrows etc and at the same time not breaking Express support for older Node versions.

Now the tests in Express are made from the examples, that seems like a really big task to rewrite for Express so instead I would suggest to remove duplicate examples into their own repo and then the tests will still cover all of the Express features.

I hope this makes sense..!

[dougwilson]

Hi @notrab I currently have it marked to merge into 4.15 branch, but that was before I realized the Node.js 0.10 support issues I noted above, so I'm not sure we can merge this at this time, rather these current changes are great, but without modification in some way would need to wait until we have a branch ready that drops Node.js 0.10 support to merge this into.

[notrab]

I've gone ahead and closed this and will create PR's for the things discussed in #3181

Please see #3222 for the first PR.