Enhancement - tab completion script

- Added a new tab completion script (thanks to Federico Hernandez).

tab_completion.sh

@@ -0,0 +1,24 @@
+_task() 
+{
+    local cur prev opts base
+
+    COMPREPLY=()
+    cur="${COMP_WORDS[COMP_CWORD]}"
+    prev="${COMP_WORDS[COMP_CWORD-1]}"
+
+    opts="add append annotate completed delete undelete info start stop done undo projects tags summary history ghistory next calendar stats import export color version help list long ls newest oldest overdue active"
+
+    case "${prev}" in
+      ls|list|long)
+        if [[ ${cur} == +* ]] ; then
+          local tags=$( task tags | egrep -v 'tags|^$'|sed 's/^/+/' )
+          COMPREPLY=( $(compgen -W "${tags}" -- ${cur}) )
+          return 0
+        fi
+        ;;
+    esac
+      
+    COMPREPLY=( $(compgen -W "${opts}" -- ${cur}) )
+    return 0
+}
+complete -F _task task