Improves ram prompt

For OS X display the sum of Pages free and Pages inactive
For Non BSD use MemAvailable instead of MemFree

powerlevel9k.zsh-theme

@@ -903,7 +903,10 @@ prompt_ram() {
   local base=''
   local ramfree=0
   if [[ "$OS" == "OSX" ]]; then
+    # Available = Free + Inactive
+    # See https://support.apple.com/en-us/HT201538
     ramfree=$(vm_stat | grep "Pages free" | grep -o -E '[0-9]+')
+    ramfree=$((ramfree + $(vm_stat | grep "Pages inactive" | grep -o -E '[0-9]+')))
     # Convert pages into Bytes
     ramfree=$(( ramfree * 4096 ))
   else
@@ -911,7 +914,7 @@ prompt_ram() {
       ramfree=$(vmstat | grep -E '([0-9]+\w+)+' | awk '{print $5}')
       base='M'
     else
-      ramfree=$(grep -o -E "MemFree:\s+[0-9]+" /proc/meminfo | grep -o "[0-9]*")
+      ramfree=$(grep -o -E "MemAvailable:\s+[0-9]+" /proc/meminfo | grep -o "[0-9]*")
       base='K'
     fi
   fi