Example fixes: no 'content' attribute for 'span' in Microdata; wrong attribute in Microdata; following recommendation for 'price' content

[unor]

This PR only changes examples:

• in Microdata, the span element can’t have a content attribute (Some Microdata examples use a 'content' attribute for 'span' #184): either omitted the element (in case where the value is the same) or used the meta element instead
• the currency symbol should not be part of the price value
• Microdata: replaced property attribute with itemprop, and used the same properties from the RDFa example (author, translator)
• RDFa: used typeof instead of typeOf

[danbri]

@unor - thanks so much! :)