added three new theme customizer options:
- switch to enable/disable featured images on archive pages
- switch to enable/disable featured images on single pages
 - switch between full content and excerpt on archive pages
Changed customizer to use checkboxes.

Added customizer settings for:
- featured image (archive)
- metadata (archive)
- full content (archive)
- featured image (single)
- metadata (single)
- author box (single)
Merge pull request #18 from kevinpapst/customizer/layout

Added theme options to show/hide featured image, excerpt, metadata in archive & single post