Updates docs for Python 3

In Python 3, the simpleHTTPServer has moved into the http module, so the command `python -m simpleHTTPServer no longer works. This minor change adds instructions for those of us using Python 3.
advertise the i18n_subsites plugin as an addition to simple translations
note that {ARTICLE,PAGE}_PATHS may include files, add faq about using that
Let documents {attach} static files. Fixes #1019.

Until now, making static files end up in the same output directory as an
article that links to them has been difficult, especially when the article's
output path is generated based on metadata. This changeset introduces the
{attach} link syntax, which works like the {filename} syntax, but also
overrides the static file's output path with the directory of the
linking document.

It also clarifies and expands the documentation on linking to internal content.
Merge pull request #1516 from foresto/static-attach

Let documents {attach} static files. Fixes #1019.
Merge pull request #1437 from mlissner/patch-1

Updates docs for Python 3
Update changelog
Increment version to 3.5
Merge branch 'master' of github.com:getpelican/pelican