rescue if execjs is present but runtime is not available
Merge 4cc92797594dd21c180456734d7f70a2a183deb7 into 6ad846e33f4a1b41d0b78812f53cc397f290aa89
minor upgrade for bootstrap-sass and tilt
set the default encoding to UTF-8
Merge pull request 277 into 0.5.0
Merge pull request 279 into 0.5.0
resolves #272 add Rakefile to generated site

- add a Rakefile to the generated site to simplify setup and execution
- add a dependency on haml since it's needed to run the generated site
- add default .awestruct_ignore to ignore Gemfile* and Rakefile