visual updates to readme
visual updates to readme

- project logo
- add link to binary
- syntax highlighting for configs
pagespeed/ngx_pagespeed,wanrui/ngx_pagespeed,0x0mar/ngx_pagespeed,0x0mar/ngx_pagespeed,digideskio/ngx_pagespeed,wanrui/ngx_pagespeed,pagespeed/ngx_pagespeed,digideskio/ngx_pagespeed