Default to <prefix>/usr/bin install.

https://bugs.gentoo.org/635032
--- a/tools/niminst/install.nimf
+++ b/tools/niminst/install.nimf
@@ -28,13 +28,13 @@ if [ $# -eq 1 ] ; then
       echo "sh deinstall.sh DIR"
       exit 1
       ;;
-    "/usr/bin")
-      bindir=/usr/bin
-      configdir=/etc/?proj
-      libdir=/usr/lib/?proj
-      docdir=/usr/share/?proj/doc
-      datadir=/usr/share/?proj/data
-      nimbleDir="/opt/nimble/pkgs/?c.nimblePkgName-?c.version"
+    *)
+      bindir=$1/usr/bin
+      configdir=$1/etc/?proj
+      libdir=$1/usr/lib/?proj
+      docdir=$1/usr/share/?proj/doc
+      datadir=$1/usr/share/?proj/data
+      nimbleDir=$1"/opt/nimble/pkgs/?c.nimblePkgName-?c.version"
       ;;
     "/usr/local/bin")
       bindir=/usr/local/bin
@@ -68,6 +68,9 @@ if [ $# -eq 1 ] ; then
       ;;
   esac
 
+  mkdir -p $bindir
+  mkdir -p $datadir
+
   mkdir -p $libdir
   mkdir -p $docdir
   mkdir -p $configdir