posterdown_html and gitnore

1. Added dynamic author and affiliation options to YAML in the posterdown_html output.

2. added more to the gitnore file to avoid bloating with unnecessary files
diff --git a/.gitignore b/.gitignore
index eaa4180..3ca391a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,3 +5,5 @@
 .Rproj.user
 *skeleton.html
 skeleton_files/
+skeleton_cahce/
+rosm.cache/