Correct BaseName Handling for Spaces in Path

This corrects "basename: extra operand ‘VAL1’" errors as seen below.
Also this moves the basename call to only occur when the help text is displayed.

> $ '/cygdrive/c/Users/myusername/OneDrive - VAL1 VAL2/Utils/github-markdown-toc/gh-md-toc' --help
> /cygdrive/c/Users/myusername/OneDrive - VAL1 VAL2/Utils/github-markdown-toc/gh-md-toc
> basename: extra operand ‘VAL1’
> Try 'basename --help' for more information.
> GitHub TOC generator (): 0.5.0
>
> Usage:
>    [--insert] src [src]  Create TOC for a README file (url or local path)
>    -                     Create TOC for markdown from STDIN
>    --help                Show help
>   --version             Show version

gh-md-toc

@@ -201,10 +201,10 @@ gh_toc_get_filename() {
 # Options hendlers
 #
 gh_toc_app() {
-    local app_name=$(basename $0)
     local need_replace="no"
 
     if [ "$1" = '--help' ] || [ $# -eq 0 ] ; then
+		local app_name=$(basename "$0")
         echo "GitHub TOC generator ($app_name): $gh_toc_version"
         echo ""
         echo "Usage:"