go1.8: support for additional features

[kardianos]

Many new important features will land in go1.8. Please see document:
https://docs.google.com/document/d/1F778e7ZSNiSmbju3jsEWzShcb8lIO4kDyfKDNm4PNd8/edit?usp=sharing for the full list.

Because these features are new we want drivers to implement them before they are released. Ideally they should be implemented by 2016-12-12 to allow for any driver provided feedback from implementation if necessary.

• Multi-Results Support Multi-Results Support #420
• ColumnType interface Implement ColumnType interface #495
• Context Interface Implement Context Interface #496
• Pinger interface Implement Pinger interface #505
• Named input parameters Add support for named input parameters #561 -- won't support

[julienschmidt]

See also #420, #495, #496 and #505

[nathany]

What about named parameter support? Shall I open a new issue for that?

[methane]

MySQL doesn't support named parameter.
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