0.4.0

• Support reading files from a Git repo #34
• Support writing files to a Git repo #35
• Improve layout on mobile.
• Rename the settings in smeagol.toml to use kebob-case, rather than
  snake_case. Specifically h1_title was renamed to h1-title and index_page
  was renamed to index-page. This matches Cargo.toml's use of kebob-case.
• Switch the index-page default value to README. This matches GitHub's
  behavior. Previously this value was Home.