Code format & syntax changes.

* `fun` keyword changed to `function`
* `seq` keyword changed to `lazy`
* Sequence functions must now use the `function` keyword.
* List comprehension syntax changed to take after Python.
* lambda arrow changed from `->` to `=>`
* `&&` changed to `and`
* `||` changed to `or`
* `==` changed to `is`
* `!=` changed to `isnt`