Adding a version number

It is shown with --help. It's also available as $MO_VERSION when mo is
sourced.

README.md

@@ -41,7 +41,7 @@ There are a few ways you can install this tool.  How you install it depends on h
 You can install this file in `/usr/local/bin/` or `/usr/bin/` by simply downloading it, changing the permissions, then moving it to the right location.  Double check that your system's PATH includes the destination folder, otherwise users may have a hard time starting the command.
 
     # Download
-    curl -sS https://git.io/get-mo -o mo
+    curl -sSL https://git.io/get-mo -o mo
 
     # Make executable
     chmod +x mo

mo

@@ -146,7 +146,7 @@ moCallFunction() {
     moArgs=()
 
     # shellcheck disable=SC2031
-    if [[ -n "$MO_ALLOW_FUNCTION_ARGUMENTS" ]]; then
+    if [[ -n "${MO_ALLOW_FUNCTION_ARGUMENTS-}" ]]; then
         moArgs=$3
     fi
 
@@ -835,15 +835,15 @@ moShow() {
 
     moSplit moNameParts "$1" "."
 
-    if [[ -z "${moNameParts[1]}" ]]; then
+    if [[ -z "${moNameParts[1]-}" ]]; then
         if moIsArray "$1"; then
             eval moJoin moJoined "," "\${$1[@]}"
             echo -n "$moJoined"
         else
             # shellcheck disable=SC2031
-            if [[ -z "$MO_FAIL_ON_UNSET" ]] || moTestVarSet "$1"; then
+            if moTestVarSet "$1"; then
                 echo -n "${!1}"
-            else
+            elif [[ -n "${MO_FAIL_ON_UNSET-}" ]]; then
                 echo "Env variable not set: $1" >&2
                 exit 1
             fi
@@ -1030,11 +1030,14 @@ moTrimWhitespace() {
 # Returns nothing.
 moUsage() {
     grep '^#/' "${MO_ORIGINAL_COMMAND}" | cut -c 4-
+    echo ""
+    set | grep ^MO_VERSION=
 }
 
 
 # Save the original command's path for usage later
 MO_ORIGINAL_COMMAND="$(cd "${BASH_SOURCE[0]%/*}" || exit 1; pwd)/${BASH_SOURCE[0]##*/}"
+MO_VERSION="2.0.4"
 
 # If sourced, load all functions.
 # If executed, perform the actions as expected.