docs: update godoc [ci skip]

godoc.md

@@ -12,7 +12,6 @@ Package tagcmp provides image tag comparison operations\.
 
 - [Variables](<#variables>)
 - [func IsParsable(tag string) bool](<#func-isparsable>)
-- [func UpgradeType(t Tag) int](<#func-upgradetype>)
 - [type ByTagAsc](<#type-bytagasc>)
   - [func (t ByTagAsc) Len() int](<#func-bytagasc-len>)
   - [func (t ByTagAsc) Less(i, j int) bool](<#func-bytagasc-less>)
@@ -28,7 +27,11 @@ Package tagcmp provides image tag comparison operations\.
   - [func (t Tag) IsGreaterThan(tag Tag) bool](<#func-tag-isgreaterthan>)
   - [func (t Tag) IsLessThan(tag Tag) bool](<#func-tag-islessthan>)
   - [func (t Tag) String() string](<#func-tag-string>)
-  - [func (curTag Tag) UpgradeElement(newTag Tag) (Tag, error)](<#func-tag-upgradeelement>)
+  - [func (curTag Tag) UpgradeDelta(newTag Tag) (TagDelta, error)](<#func-tag-upgradedelta>)
+- [type TagDelta](<#type-tagdelta>)
+  - [func ParseDelta(delta string) (TagDelta, error)](<#func-parsedelta>)
+  - [func (t TagDelta) String() string](<#func-tagdelta-string>)
+  - [func (d TagDelta) UpgradeType() int](<#func-tagdelta-upgradetype>)
 
 
 ## Variables
@@ -71,14 +74,6 @@ func IsParsable(tag string) bool
 
 IsParsable determines if a tag is supported by this library
 
-## func UpgradeType
-
-```go
-func UpgradeType(t Tag) int
-```
-
-UpgradeType takes exit from UpgradeElemene and returns a numeric representation of upgrade or downgrade 1/\-1: patch 2/\-2: minor 4/\-4: major 0: no change
-
 ## type ByTagAsc
 
 ByTagAsc sorts tags in ascending order where the last element is the latest tag\.
@@ -140,8 +135,9 @@ type Tag struct {
     MissingMinor bool   // whether or not the minor semver part was left out
     Patch        string `json:",omitempty"` // patch semver part
     MissingPatch bool   // whether or not he patch semver part was left out
-    Suffix       string // tag suffix (e.g. "-alpine")
+    Suffix       string // tag suffix (e.g. "-alpine") [would be release candidate in semver]
     UsesV        bool   // whether or not the tag uses the "v" prefix
+    Metadata     string // metadata: what's after + and after the first "-"
 }
 ```
 
@@ -193,13 +189,45 @@ func (t Tag) String() string
 
 String formats a Tag correctly in string representation
 
-### func \(Tag\) UpgradeElement
+### func \(Tag\) UpgradeDelta
 
 ```go
-func (curTag Tag) UpgradeElement(newTag Tag) (Tag, error)
+func (curTag Tag) UpgradeDelta(newTag Tag) (TagDelta, error)
 ```
 
-UpgradeElement returns a Tag object which is the difference between an old and new tag It can contain negative numbers if comparing with an older tag\.
+UpgradeDelta returns a TagDelta object which is the difference between an old and new tag It can contain negative numbers if comparing with an older tag\.
+
+## type TagDelta
+
+```go
+type TagDelta struct {
+    Major int // major semver difference
+    Minor int // minor semver difference
+    Patch int // patch semver difference
+}
+```
+
+### func ParseDelta
+
+```go
+func ParseDelta(delta string) (TagDelta, error)
+```
+
+ParseDelta converts a tag difference in the format of X\, X\.Y or X\.Y\.Z where X\, Y\, Z are positive or negative integers or 0
+
+### func \(TagDelta\) String
+
+```go
+func (t TagDelta) String() string
+```
+
+### func \(TagDelta\) UpgradeType
+
+```go
+func (d TagDelta) UpgradeType() int
+```
+
+UpgradeType takes exit from UpgradeElemene and returns a numeric representation of upgrade or downgrade 1/\-1: patch 2/\-2: minor 4/\-4: major 0: no change