Implement a more configurable modeline

Closes #40
Remove unnecessary PROGN
Use alexandria:when-let* instead of a more clunky construct
No need to manually pass the URI into the modeline

It happens automatically now, additional specifiers can be used outside
of this.
Add modeline back into the browser
No need for a new binding, an accessor exists
Merge pull request #57 from AeroNotix/alf-implement-a-better-modeline

Implement a more configurable modeline