AssignLink reinstated in NodeAssembler.

(Probably should've done this a while ago.  Much earlier in this
research branch, I thought the design of Link/LinkBuilder etc might
get a review... but at this point, its clear there's plenty of
work already do to just sorting out the assembler situation, so
any rethinks of links is *definitely* deferred for future investigation
(if indeed anything ever happens there at all).)

Doing very partial fixes to the example "generated" maps;
just enough to compile.  I'm not intending to use them as a template
for actual codegen later, so their quality is irrelevant at this point.

_rsrch/nodesolution/impls/any.go

@@ -105,6 +105,9 @@ func (nb *anyBuilder) AssignString(v string) error {
 func (nb *anyBuilder) AssignBytes(v []byte) error {
 	panic("soon")
 }
+func (nb *anyBuilder) AssignLink(v ipld.Link) error {
+	panic("soon")
+}
 func (nb *anyBuilder) AssignNode(v ipld.Node) error {
 	// TODO what to do here?  should we just... keep it, in another `Node` field?
 	panic("soon")

_rsrch/nodesolution/impls/int.go

@@ -135,6 +135,9 @@ func (na *plainInt__Assembler) AssignNode(v ipld.Node) error {
 		return nil
 	}
 }
+func (plainInt__Assembler) AssignLink(ipld.Link) error {
+	return mixins.IntAssembler{"int"}.AssignLink(nil)
+}
 func (plainInt__Assembler) Style() ipld.NodeStyle {
 	return Style__Int{}
 }

_rsrch/nodesolution/impls/map.go

@@ -197,6 +197,9 @@ func (na *plainMap__Assembler) AssignNode(v ipld.Node) error {
 	//   (wait... actually, probably we can?  'Assign' is a "finish" method.  we can&should invalidate the wip pointer here.)
 	panic("later")
 }
+func (plainMap__Assembler) AssignLink(ipld.Link) error {
+	return mixins.MapAssembler{"map"}.AssignLink(nil)
+}
 func (plainMap__Assembler) Style() ipld.NodeStyle { panic("later") }
 
 // -- MapNodeAssembler -->
@@ -301,6 +304,9 @@ func (mka *plainMap__KeyAssembler) AssignString(v string) error {
 func (plainMap__KeyAssembler) AssignBytes([]byte) error {
 	return mixins.StringAssembler{"string"}.AssignBytes(nil)
 }
+func (plainMap__KeyAssembler) AssignLink(ipld.Link) error {
+	return mixins.StringAssembler{"string"}.AssignLink(nil)
+}
 func (mka *plainMap__KeyAssembler) AssignNode(v ipld.Node) error {
 	vs, err := v.AsString()
 	if err != nil {
@@ -334,6 +340,7 @@ func (mva *plainMap__ValueAssembler) AssignString(v string) error {
 	return mva.AssignNode(&vb)
 }
 func (mva *plainMap__ValueAssembler) AssignBytes([]byte) error   { panic("todo") }
+func (mva *plainMap__ValueAssembler) AssignLink(ipld.Link) error { panic("todo") }
 func (mva *plainMap__ValueAssembler) AssignNode(v ipld.Node) error {
 	l := len(mva.ma.w.t) - 1
 	mva.ma.w.t[l].v = v

_rsrch/nodesolution/impls/map_K_T.go

@@ -359,6 +359,7 @@ func (_Map_K_T__Assembler) AssignInt(v int) error                           { pa
 func (_Map_K_T__Assembler) AssignFloat(float64) error                       { panic("no") }
 func (_Map_K_T__Assembler) AssignString(v string) error                     { panic("no") }
 func (_Map_K_T__Assembler) AssignBytes([]byte) error                        { panic("no") }
+func (_Map_K_T__Assembler) AssignLink(ipld.Link) error                      { panic("no") }
 func (ta *_Map_K_T__Assembler) AssignNode(v ipld.Node) error {
 	if v2, ok := v.(*Map_K_T); ok {
 		*ta.w = *v2
@@ -452,6 +453,7 @@ func (mka *_Map_K_T__KeyAssembler) AssignString(v string) error {
 	return nil
 }
 func (_Map_K_T__KeyAssembler) AssignBytes([]byte) error   { panic("no") }
+func (_Map_K_T__KeyAssembler) AssignLink(ipld.Link) error { panic("no") }
 func (mka *_Map_K_T__KeyAssembler) AssignNode(v ipld.Node) error {
 	vs, err := v.AsString()
 	if err != nil {
@@ -479,6 +481,7 @@ func (mva *_Map_K_T__ValueAssembler) AssignInt(v int) error {
 func (mva *_Map_K_T__ValueAssembler) AssignFloat(float64) error   { panic("todo") }
 func (mva *_Map_K_T__ValueAssembler) AssignString(v string) error { panic("todo") }
 func (mva *_Map_K_T__ValueAssembler) AssignBytes([]byte) error    { panic("todo") }
+func (mva *_Map_K_T__ValueAssembler) AssignLink(ipld.Link) error  { panic("todo") }
 func (mva *_Map_K_T__ValueAssembler) AssignNode(v ipld.Node) error {
 	if err := mva.ca.AssignNode(v); err != nil {
 		return err

_rsrch/nodesolution/impls/string.go

@@ -132,6 +132,9 @@ func (na *plainString__Assembler) AssignString(v string) error {
 func (plainString__Assembler) AssignBytes([]byte) error {
 	return mixins.StringAssembler{"string"}.AssignBytes(nil)
 }
+func (plainString__Assembler) AssignLink(ipld.Link) error {
+	return mixins.StringAssembler{"string"}.AssignLink(nil)
+}
 func (na *plainString__Assembler) AssignNode(v ipld.Node) error {
 	if s, err := v.AsString(); err != nil {
 		return err

_rsrch/nodesolution/nodeBuilder.go

@@ -24,6 +24,7 @@ type NodeAssembler interface {
 	AssignFloat(float64) error
 	AssignString(string) error
 	AssignBytes([]byte) error
+	AssignLink(Link) error
 
 	AssignNode(Node) error // if you already have a completely constructed subtree, this method puts the whole thing in place at once.