Fixed lint issues and missing documentation

internal/types/classifications.go

@@ -1,5 +1,9 @@
 package types
 
+// ClassificationCode is a code classifying what an opportunity buys. IsCPV
+// says the code is from the Common Procurement Vocabulary; Classification is
+// its description. ID is the database row, shared by every opportunity with
+// the same code.
 type ClassificationCode struct {
 	ID             int64  `db:"id"             json:"id"`
 	IsCPV          bool   `db:"is_cpv"         json:"is_cpv"`

internal/types/opportunities.go

@@ -26,6 +26,8 @@ type Opportunity struct {
 	Releases          []OpportunityRelease `db:"-"                   json:"releases"`
 }
 
+// OpportunityRelease is one OCDS release of an opportunity. JSON holds the
+// whole release as received; releases are never changed once stored.
 type OpportunityRelease struct {
 	UUID        string                  `db:"uuid"         json:"uuid"`
 	ReleaseID   string                  `db:"release_id"   json:"release_id"`
@@ -34,6 +36,8 @@ type OpportunityRelease struct {
 	JSON        string                  `db:"data"         json:"data"`
 }
 
+// OpportunityReleaseTag is one of a release's OCDS tags, e.g. "tender" or
+// "award".
 type OpportunityReleaseTag struct {
 	UUID      string `db:"uuid"       json:"uuid"`
 	ReleaseID string `db:"release_id" json:"release_id"`