Sync README w/ dev portal for Data API v2.3.5

[mDuo13]

• Remove the "Get Capitalization" method docs to match the code
• Sync up some minor differences like mentions of removed fields
• Remove link from ToC to removed "Get Issued Value" method
• Match whitespace in the dev portal version ( https://github.com/ripple/ripple-dev-portal/blob/master/content/references/data-api.md )
• Match URL templating convention (RFC6570) to dev portal