adding some of the considerations from issue #4
making the text more readable
adding a link to the JS techincal details
added something about click tags and geo apis
Updated height, width and size.
Fixing typos.
Clarifying language
Adding currently available banner format.
Update 2. Limitations

Added new limitations regarding javascript events. Minor adjustments to
copy.
Removing the bullet Box from list of Dimensions.
added something about click tags and geo apis
moving styling tips
merging changes and adjusting headline
Merge pull request #7 from finn-no/techdetails

merging in some technical details added to clarify why certain things are in the specification