Remaining commands

[ConnorAtherton]

These are commands that are present in GNU Readline but not rb-readline. Reported in #108.

copy-backward-word
copy-forward-word
do-uppercase-version
dump-functions
dump-macros
dump-variables
end-of-file
history-search-backward (not the same as backward-search-history)
history-search-forward (not the same as forward-search-history)
history-substr-search-backward
history-substr-search-forward
kill-region
menu-complete
menu-complete-backward
prefix-meta
print-last-kbd-macro
skip-csi-sequence