Fix substitution for hiding contexts/projects

When using the -+ or -@ option to hide project or context names in list
output, the color reset sequence was being deleted if the project/context
was at the end of the line.

For example, with the following tasks:

    (B) with priority, ending in a +project
    task that shouldn't be highlighted

Running 'todo.sh -+ list' would hide the "+project" from the first task,
but would also remove the color reset sequence ^[[0m at the end.  The
color from the prioritized task would continue to the next lines.

This commit fixes the problem and adds a test to verify the fix.

todo.sh

@@ -360,7 +360,7 @@ do
             unset HIDE_CONTEXTS_SUBSTITUTION
         else
             ## One or odd value -- hide context names
-            export HIDE_CONTEXTS_SUBSTITUTION='[[:space:]]@[^[:space:]]\{1,\}'
+            export HIDE_CONTEXTS_SUBSTITUTION='[[:space:]]@[[:graph:]]\{1,\}'
         fi
         ;;
     '+' )
@@ -376,7 +376,7 @@ do
             unset HIDE_PROJECTS_SUBSTITUTION
         else
             ## One or odd value -- hide project names
-            export HIDE_PROJECTS_SUBSTITUTION='[[:space:]][+][^[:space:]]\{1,\}'
+            export HIDE_PROJECTS_SUBSTITUTION='[[:space:]][+][[:graph:]]\{1,\}'
         fi
         ;;
     a )