Add support for braille terminal (#310)

* Add support for braille terminal

fixes #307

* Add braille to Readme

* quote tidying

* currently requires sdl display

noted in the docs rather than forcing so if Qemu and/or brtty provide
a solution we will get immediate or easy benefit.

* add needed sdl to braille examples

quickemu

@@ -907,6 +907,12 @@ function vm_boot() {
          -monitor none
          -serial mon:stdio)
 
+  if [[ "${ACCESSIBLE}" == "braille" ]] || [[ "${ACCESSIBLE}" == "brl" ]]; then
+    # shellcheck disable=SC2054
+      args+=(-chardev braille,id=brltty
+             -device usb-braille,id=usbbrl,chardev=brltty)
+  fi
+
   if [ -n "${bridge}" ]; then
     # Enable bridge mode networking
     # shellcheck disable=SC2054,SC2206
@@ -1049,6 +1055,7 @@ function usage() {
   echo "  ${LAUNCHER} --vm ubuntu.conf"
   echo
   echo "You can also pass optional parameters"
+  echo "  --accessible            : Select accessible facilitation. 'braille' (default - currently requires --display sdl )"
   echo "  --delete-disk           : Delete the disk image and EFI variables"
   echo "  --delete-vm             : Delete the entire VM and it's configuration"
   echo "  --display               : Select display backend. 'sdl' (default), 'gtk', 'none', or 'spice'"
@@ -1065,6 +1072,14 @@ function usage() {
   exit 1
 }
 
+#
+function accessible_param_check() {
+  if [ "${ACCESSIBLE}" != "braille" ] && [ "${ACCESSIBLE}" != "brl" ] ; then
+    echo "ERROR! Requested accessiblility '${ACCESSIBLE}' is not recognised."
+    exit 1
+    # TODO can we check the device/API is available
+  fi
+}
 function display_param_check() {
   if [ "${OUTPUT}" != "gtk" ] && [ "${OUTPUT}" != "none" ] && [ "${OUTPUT}" != "sdl" ] && [ "${OUTPUT}" != "spice" ]; then
     echo "ERROR! Requested output '${OUTPUT}' is not recognised."
@@ -1155,6 +1170,11 @@ if [ $# -lt 1 ]; then
 else
     while [ $# -gt 0 ]; do
         case "${1}" in
+          -acc|--acc|-accessible|--accessible|-accessibility|--accessibility)
+            ACCESSIBLE="${2}"
+            accessible_param_check
+            shift
+            shift;;
           -delete|--delete|-delete-disk|--delete-disk)
             DELETE_DISK=1
             shift;;