add level 4 spells

spells/Air3.tex

 \spell{Putrid Visage}% Name
-  {\mWater}% Spheres
+  {\mAir}% Spheres
   {Wane}% Action
   {\detailed,\duplicated}% Enhancements
   {wind speed}% Resist with

spells/Air4.tex

+\spell{Safe Passage}% Name
+  {\mAir}% Spheres
+  {Warp}% Action
+  {\detailed, \distant, \duplicated}% Enhancements
+  {wind or tide's potence}% Resist with
+  {a path appears, surrounded by clouds, which repels anything which might harm those who walk it (projectiles receive a minus \arabic{spelllevel} penalty, and other attacks receive minus \arabic{spelllevel} \glspl{ap}}% Description
+  {
+    The caster calls `make way, make safe', and the wind begins to form a path.
+    Gusts of cloud begin to form, and soon settle, creating a comforting mist along the path.
+
+    Anyone firing projectiles onto the misty path receives a minus \arabic{spelllevel} penalty due to lack of vision, and the same again due to the protective funnel of wind buffering the arrows back.
+    The path begins \spellRange\ away, and covers about the same length from that point onwards.
+}
+