Document livereload usage in config file
Suggest adding middleman-livereload to bundle
unrequire osx file watcher
Allow frontmatter renderer_options key to overwrite renderer options on a per-file basis. closes #859
Support sideloading from .frontmatter files. Closes #855
prep 3.1 beta
Add Sprockets changes to CHANGELOG
Simplify configuration a bit, and make extensions raise an error if the user tries to set an invalid extension option.
Fix location of meta pages in CHANGELOG
Update the extension template for the new Extension class.
Requiring sinatra messes stuff up
Rewrite asset hash extension with new extension class
In general, no need for bundle exec since we call bundle/setup
Save information about extensions in a discoverable way.

This allows us to display extension config information at /__middleman/config/, and also allows users to modify extension
settings after they're activated in config.rb with a statement like "extensions[:asset_hash].options.exts += ['.js']".
Reorganize Request a bit
Add in the metadata rack app early so it is there whenever middleware grabs the app
Add extensions to meta config page
Advertise meta pages on startup
Default build to cleaning
Merge pull request #862 from middleman/default_clean_true

Default build to --clean