Merge pull request #6 from snarfed/master

send webmentions with Accept */*, not application/json
Changed sending webmentions HTTP headers.

send webmentions with Accept */*, not application/json
Merge branch 'master' of https://github.com/snarfed/webmention-tools

Discover webmention endpoints in the Link HTTP response header
also don't verify SSL certs. python-requests's verification is overly
aggressive.
Fixes #7. thanks again for the find, @jeena!
Merge pull request #9 from snarfed/master

add endpoint kwarg to WebmentionSend ctor
discover webmention endpoints in <a> tags as well as <link>

background: converspace/webmention#32