Cannot clear unmodifiable maps

Signed-off-by: Clement Escoffier <clement.escoffier@gmail.com>
Fix #108

Shell prompt accessible using -Dshell or -Dinteractive
'exit' command to leave.

Signed-off-by: Clement Escoffier <clement.escoffier@gmail.com>
Cosmetic fix

Signed-off-by: Clement Escoffier <clement.escoffier@gmail.com>