[string/encoding] Adding missing =back pod statements

This fixes pod errors found by podchecker

src/string/encoding.c

@@ -498,6 +498,11 @@ Parrot_default_encoding(SHIM_INTERP)
     return Parrot_default_encoding_ptr;
 }
 
+/*
+
+=back
+
+*/
 
 /*
  * Local variables:

src/string/encoding/ascii.c

@@ -444,6 +444,11 @@ static STR_VTABLE Parrot_ascii_encoding = {
 
 STR_VTABLE *Parrot_ascii_encoding_ptr = &Parrot_ascii_encoding;
 
+/*
+
+=back
+
+*/
 
 /*
  * Local variables:

src/string/encoding/binary.c

@@ -242,6 +242,11 @@ static STR_VTABLE Parrot_binary_encoding = {
 
 STR_VTABLE *Parrot_binary_encoding_ptr = &Parrot_binary_encoding;
 
+/*
+
+=back
+
+*/
 
 /*
  * Local variables:

src/string/encoding/latin1.c

@@ -472,6 +472,11 @@ static STR_VTABLE Parrot_latin1_encoding = {
 
 STR_VTABLE *Parrot_latin1_encoding_ptr = &Parrot_latin1_encoding;
 
+/*
+
+=back
+
+*/
 
 /*
  * Local variables:

src/string/encoding/null.c

@@ -180,6 +180,11 @@ static STR_VTABLE Parrot_null_encoding = {
 
 STR_VTABLE *Parrot_null_encoding_ptr = &Parrot_null_encoding;
 
+/*
+
+=back
+
+*/
 
 /*
  * Local variables:

src/string/encoding/shared.c

@@ -1684,6 +1684,12 @@ unicode_titlecase_first(PARROT_INTERP, SHIM(const STRING *src))
         "Unicode titlecase_first not implemented");
 }
 
+/*
+
+=back
+
+*/
+
 
 /*
  * Local variables: