Release v0.4.0

Changes since v0.3.0

API

• List files & directories for collection & page APIs #281 .
• Only allow files that render to HTML to be written as a Page #301 (props to @ivantsepp )

User Interface

• Add tooltip to path input about autogenerating #291
• Clear errors before unmounting #296 (performance)
• Interface improvements #308 #309 (props to @ashmaroli )

Development

• Migrate to Webpack 2 #298

Documentation

• Minor documentation edits by @ashmaroli #286
• Update repo screenshot #293