doc/hacking: inline gists directly in the document

Instead of referring to external resources, the document is now more
self-contained. I felt that the patches were sufficiently simple that
they were better expressed as editing instructions. The advantage of
plain text editing instructions is that anybody can apply them without
having to know how to use patch(1).
doc/hacking: break long line

Python's ConfigParser module allows line breaks in values when the
continuation lines are indented. Testing this shows that Swift is okay
with the newlines.
doc/hacking: be more explicit about what was inserted
Merge pull request #75 from mgeisler/include-gists

Inline gists in hacking document