Adds nice to Backtrace refs #2809

doc/Type/Backtrace.pod6

@@ -24,6 +24,13 @@ if ($!) {
 This will print the last dataframe in the list, pointing at the line where it's
 happened.
 
+=for code
+sub zipi { { { die "Something bad happened" }() }() };
+try zipi;
+say $!.backtrace.nice( :oneline ) if $!                           │
+# OUTPUT: «  in sub zipi at /tmp/Ik2MevkgP1 line 1␤␤»
+
+
 =head1 Methods
 
 =head2 method new
@@ -48,7 +55,7 @@ be used instead of the current code.
 
 Defined as:
 
-    multi method gist(Backtrace:D: --> Str:D)
+    multi method gist(Backtrace:D:)
 
 Returns string C<"Backtrace(42 frames)"> where the number indicates the number
 of frames available via L<list|/routine/list> method.
@@ -66,6 +73,15 @@ the implementation, also some routines from the setting.
     my $backtrace = Backtrace.new;
     say $backtrace.Str;
 
+=head2 method nice
+
+Defined as:
+
+    method nice(Backtrace:D: :$oneline)
+
+Returns the backtrace as a list of I<interesting> frames. If C<:$oneline> is
+set, will stop after the first frame.
+
 =head2 method full
 
 Defined as: