Change Ctrl-C and move old behavior to Ctrl-Q

This lets Janet be a better unix citizen and lets Ctrl-C
raise an interrupt. Trying to make Janet behave superficially
like a shell by overriding Ctrl-C is not helpful.

CHANGELOG.md

@@ -2,6 +2,8 @@
 All notable changes to this project will be documented in this file.
 
 ## Unreleased - ???
+- Change repl behavior to make Ctrl-C raise SIGINT on posix. The old behavior for Ctrl-C,
+  to clear the current line buffer, has been moved to Ctrl-Q.
 - Importing modules that start with `/` is now the only way to import from project root.
   Before, this would import from / on disk.
 - Change hash function for numbers.

janet.1

@@ -64,6 +64,10 @@ Move cursor to the beginning of input line.
 .BR Ctrl\-B
 Move cursor one character to the left.
 
+.TP 16
+.BR Ctrl\-D
+If on a newline, indicate end of stream and exit the repl.
+
 .TP 16
 .BR Ctrl\-E
 Move cursor to the end of input line.
@@ -100,6 +104,10 @@ Delete one word before the cursor.
 .BR Ctrl\-G
 Show documentation for the current symbol under the cursor.
 
+.TP 16
+.BR Ctrl\-Q
+Clear the current command, including already typed lines.
+
 .TP 16
 .BR Alt\-B/Alt\-F
 Move cursor backwards and forwards one word.

src/mainclient/shell.c

@@ -758,6 +758,10 @@ static int line() {
                 kleft();
                 break;
             case 3:     /* ctrl-c */
+                clearlines();
+                gbl_sigint_flag = 1;
+                return -1;
+            case 17:    /* ctrl-q */
                 gbl_cancel_current_repl_form = 1;
                 clearlines();
                 return -1;