update User object to OpenRTB 2.6 for EIDs (#45)

Update impression.go

Merge pull request #40 from UnityTech/PPS-361

PPS-361 Remove Omitempty

Merge pull request #38 from UnityTech/custom_type_reg_ext_lgpd

Handle incoming bool/int fields for lgpd

use RegExtension regs.ext as it was prior to pulling in upstream chan…

…ges (#37)

Change AppStartTime to be of type int64

Merge pull request #24 from UnityTech/add/appstarttime-userextension

Add AppStartTime to UserExtension struct.

Merge pull request #16 from UnityTech/APIN-2184

[APIN-2184] add field for CCPA

Merge pull request #39 from emaraschio/master

bidrequest: Add new fields related to seats from 2.5 Spec

Merge pull request #34 from marklr/master

Add support for stringified imp.secure attribute