wheel: make sure destination path exists
include test installing headers
write something about whether binary wheels go on pypi
Update cookbook.rst
Merge pull request #956 from dholth/develop

write something about whether binary wheels go on pypi
have cleanup be in a finally after wheel building
remove 'pip wheel --unpack-only'
--no-clean for 'pip wheel'
Merge pull request #958 from qwcode/wheel_cleanup

Wheel cleanup
single definition of find_links
install wheel from local packages in tests
Fix unpack_http_url for already downloaded files

mimetypes.guess_type returns a tuple (type, encoding),
so, use element number 0 as content_type.

Otherwise, TypeError is raised in cache_download
(cannot write a tuple to file).