Support $_Z_DATA environment variable (#545)

Support `$_Z_DATA` environment variable per z's documentation dcd5541e7d/z.1 (L78).
`$_Z_DATA` allows changing the default location of the z database file.

plugins/fzz

@@ -15,11 +15,12 @@ else
     exit 1
 fi
 
-if [ -f "$HOME/.z" ]; then
+datafile="${_Z_DATA:-$HOME/.z}"
+if [ -f "$datafile" ]; then
     # I read the data from z's file instead of calling the z command so that the data doesn't need to be processed twice
-    sel=$(awk -F "|" '{print $1}' "$HOME/.z" | "$fuzzy" | awk '{$1=$1};1')
+    sel=$(awk -F "|" '{print $1}' "$datafile" | "$fuzzy" | awk '{$1=$1};1')
     # NOTE: Uncomment this line and comment out the line above if you want to see the weightings of the dir's in the fzf/fzy pane
-    # sel=$(awk -F "|" '{printf "%s %s\n", $2, $1}' "$HOME/.z" | "$fuzzy" | sed 's/^[0-9,.]* *//' | awk '{$1=$1};1')
+    # sel=$(awk -F "|" '{printf "%s %s\n", $2, $1}' "$datafile" | "$fuzzy" | sed 's/^[0-9,.]* *//' | awk '{$1=$1};1')
 else
     exit 1
 fi