Add support to batch statements for http driver

[luisfvieirasilva]

To accomplish that this commmit does:

• Implement RowsNextResultSet interface
• Split statements into multiple ones
• Split parameters correctly for each statement
• Deal with positional parameters

[haaawk]

@luisfvieirasilva you created a commit that changes 28 files and 35k lines. Is it really one big thing that can't be split into smaller self contained commits?

[haaawk]

Also I don't know what was generated and what not. Can't we use go generate and not check in generated code?

[luisfvieirasilva]

@haaawk PR updated