Add key bindings for PgUp and PgDn (#509)

* Add key bindings for PgUp, PgDn

* Match behavior of readline 8.2

In the latest readline (8.2), page-up and page-down are bound to
history-search-backward and history-search-forward by default.

We would like reline to have the same default behavior.

lib/reline/ansi.rb

@@ -8,6 +8,8 @@ class Reline::ANSI
     'khome' => :ed_move_to_beg,
     'kend'  => :ed_move_to_end,
     'kdch1' => :key_delete,
+    'kpp' => :ed_search_prev_history,
+    'knp' => :ed_search_next_history,
     'kcuu1' => :ed_prev_history,
     'kcud1' => :ed_next_history,
     'kcuf1' => :ed_next_char,

test/reline/test_ansi_with_terminfo.rb

@@ -33,6 +33,20 @@ def test_kdch1
     omit e.message
   end
 
+  # PgUp key
+  def test_kpp
+    assert_key_binding(Reline::Terminfo.tigetstr('kpp'), :ed_search_prev_history)
+  rescue Reline::Terminfo::TerminfoError => e
+    omit e.message
+  end
+
+  # PgDn key
+  def test_knp
+    assert_key_binding(Reline::Terminfo.tigetstr('knp'), :ed_search_next_history)
+  rescue Reline::Terminfo::TerminfoError => e
+    omit e.message
+  end
+
   # Up arrow key
   def test_kcuu1
     assert_key_binding(Reline::Terminfo.tigetstr('kcuu1'), :ed_prev_history)