new_tex_document, cdsc_tex_aliases.sh: assignment -> memo

Update the script and the alias file to match the rename of
assignment_template to memo_template. The 'assignment' type is
replaced by 'memo' in new_tex_document; the new_tex_assignment
alias becomes new_tex_memo.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

new_tex_document

@@ -10,7 +10,7 @@ CURDIR=$(pwd)
 
 usage() {
     echo "Usage: $(basename "$0") <type> <directory>"
-    echo "Types: paper, assignment, knitr, letter"
+    echo "Types: paper, memo, knitr, letter"
     exit 1
 }
 
@@ -26,10 +26,10 @@ case "$TYPE" in
         TEMPLATE="paper_template"
         EXT="tex"
         ;;
-    assignment)
+    memo)
         REPO="$HOME/tex/cdsc_tex"
         BRANCH="master"
-        TEMPLATE="assignment_template"
+        TEMPLATE="memo_template"
         EXT="tex"
         ;;
     knitr)