Support C-x C-e combo on shell prompt

[jaromil]

Test and document in-line usage in a shell prompt using piping and C-x C-e
Bash manual recites:

Invoke an editor on the current command line, and execute the result as shell commands. Bash attempts to invoke $VISUAL, $EDITOR, and emacs as the editor, in that order.

So cjit can quickly execute commands using:

cat << EOF | cjit [C-x C-e]
[hack away with your C code here
EOF