release v0.030

 - cache file store's realpath to fix race condition
 - require frontmatter to begin with '---'
 - rename statocles site documents to .markdown
 - rename documents from '.yml' to '.markdown'
 - make all file stores ignore other stores' files
 - rename Store to Store::File
 - ignore hidden files in the static app
 - only allow html files in the sitemap.xml
 - reset STDIN to the tty when piping in content
 - put the full changelog behind a click
 - add release announcement for v0.029