pod: add missing punctuation in doc files

pod/perl589delta.pod

@@ -1307,7 +1307,7 @@ char-classes as an escaping mechanism will see a speedup. (Yves Orton)
 
 =item *
 
-Creating anonymous array and hash references (ie. C<[]> and C<{}>) now incurs
+Creating anonymous array and hash references (i.e. C<[]> and C<{}>) now incurs
 no more overhead than creating an anonymous list or hash. Nicholas Clark
 provided changes with a saving of two ops and one stack push, which was measured
 as a slightly better than 5% improvement for these operations.

pod/perlfunc.pod

@@ -5463,7 +5463,7 @@ of values, as follows:
        as possible.  Bit eight (the high bit) is set on each byte
        except the last.
 
-    x  A null byte (a.k.a ASCII NUL, "\000", chr(0))
+    x  A null byte (a.k.a. ASCII NUL, "\000", chr(0))
     X  Back up a byte.
     @  Null-fill or truncate to absolute position, counted from the
        start of the innermost ()-group.

pod/perlsyn.pod

@@ -550,7 +550,7 @@ If the size of the LIST is not an exact multiple of the number of iterator
 variables, then on the last iteration the "excess" iterator variables are
 aliases to C<undef>, as if the LIST had C<, undef> appended as many times as
 needed for its length to become an exact multiple.  This happens whether
-LIST is a literal LIST or an array - ie arrays are not extended if their
+LIST is a literal LIST or an array - i.e. arrays are not extended if their
 size is not a multiple of the iteration size, consistent with iterating an
 array one-at-a-time.  As these padding elements are not lvalues, attempting
 to modify them will fail, consistent with the behaviour when iterating a