.mdwn -> .markdown

Signed-off-by: Jim Pryor <profjim@jimpryor.net>

diff --git a/index.mdwn b/index.markdown
similarity index 100%
rename from index.mdwn
rename to index.markdown

diff --git a/index/discussion.mdwn b/index/discussion.markdown
similarity index 100%
rename from index/discussion.mdwn
rename to index/discussion.markdown