* 4. Summary of commands.
 *
 *  CURSOR MOTION
 *    up-arrow  Move cursor 1 line up.  At top of screen, reverse scroll
 *    down-arrow  Move cursor 1 line down.  At bottom, scroll forward.
 *    left-arrow  Move cursor 1 character left or to end of previous line
 *    right-arrow Move cursor 1 character right or to start of next line
 *    CTRL-A   Move cursor to start of current line
 *    CTRL-Z   Move cursor to end of current line
 *    CTRL-^   Move cursor to top of screen
 *    CTRL-_   Move cursor to bottom of screen
 *    CTRL-F   Forward to start of next word (even to next line)
 *    CTRL-B   Backward to first character of previous word
 *
 *  SCREEN MOTION
 *    Home key  Move cursor to first character of file
 *    End key   Move cursor to last character of file
 *    PgUp    Scroll backward 1 page. Bottom line becomes top line
 *    PgD    Scroll backward 1 page. Top line becomes bottom line
 *    CTRL-D   Scroll screen down one line (reverse scroll)
 *    CTRL-U   Scroll screen up one line (forward scroll)
 *
 *  MODIFYING TEXT
 *    ASCII char  Self insert character at cursor
 *    tab    Insert tab at cursor
 *    backspace  Delete the previous char (left of cursor), even line feed
 *    Del    Delete the character under the cursor
 *    CTRL-N   Delete next word
 *    CTRL-P   Delete previous word
 *    CTRL-O   Insert line feed at cursor and back up 1 character
 *    CTRL-T   Delete tail of line (cursor to end); if empty, delete line
 *    CTRL-@   Set the mark (remember the current location)
 *    CTRL-K   Delete text from the mark to current position save on file
 *    CTRL-C   Save the text from the mark to the current position
 *    CTRL-Y   Insert the contents of the save file at current position
 *    CTRL-Q   Insert the contents of the save file into a new file
 *    CTRL-G   Insert a file at the current position
 *
 *  MISCELLANEOUS
 *    CTRL-E   Erase and redraw the screen
 *    CTRL-V   Visit file (read a new file); complain if old one changed
 *    CTRL-W   Write the current file back to the disk
 *    numeric +  Search forward (prompt for regular expression)
 *    numeric -  Search backward (prompt for regular expression)
 *    numeric 5  Print the current status of the file
 *    CTRL-R   (Global) Replace str1 by str2 (prompts for each string)
 *    CTRL-L   (Line) Replace string1 by string2
 *    CTRL-S   Fork off a shell and wait for it to finish
 *    CTRL-X   EXIT (prompt if file modified)
 *    CTRL-]   Go to a line. Prompts for linenumber
 *    CTRL-\   Abort whatever editor was doing and start again
 *    escape key  Repeat a command count times; (prompts for count)