AmEx cards actually start with 34 or 37

Here's one you can try: 340000000000009
Merge pull request #55 from shezi/patch-2

AmEx cards actually start with 34 or 37
Fixes bootstrap 2.3 issue noted by @shezi on #54; potentially addresses #32 as well.
Updated README to include note about submitting compiled SCSS and CS.
Updated README with PR requirements for card layouts, etc.
Fixed formatting slightly; hoping this fixes the screenshot.
Updated product images; added original src images.
Removed unused Amex black card face.
Composited background images are now working + preloaded; fixed #31 for the time being.
Fixes bug with IE10 selectionRange on inactive field.
Merge branch 'master' into gh-pages