Better horizontal acceleration courtesy of Alex M.

src/player.c

@@ -6,30 +6,42 @@
 #include "raylib.h"
 
 // let's a go!
-
+float curhorvel=0.0f; //current horizonatal velocity
 void UpdatePlayerControls(void)
 {
     // if there isn't a player, you probably can't do much
-    if (!player)
+    if (!player){
         return;
-
+    }
+    if(curhorvel==0.0f){
+        curhorvel=10.0f*scale;
+    }
     // if a key pressed, push player to the left
     if (IsKeyDown(KEY_A))
     {
+        if(curhorvel<PMV){
+            curhorvel=curhorvel*PLAYER_SPEED_FACTOR;
+        }
         ApplyForce(
             player,
-            (Vector2){-PLAYER_FORCE, 0}
+            (Vector2){-curhorvel, 0}
         );
     }
     // if d key pressed, push player to the right
-    if (IsKeyDown(KEY_D))
+    else if (IsKeyDown(KEY_D))
     {
+        if(curhorvel<=PMV){
+            curhorvel=curhorvel*PLAYER_SPEED_FACTOR;
+        }
         ApplyForce(
             player,
-            (Vector2){PLAYER_FORCE, 0}
-        );
+            (Vector2){curhorvel, 0}
+       );
     }
-    // if sspace key pressed (and player isn't already jumping), push player upward
+    else{
+        curhorvel=10.0f*scale;
+    }
+    // if sspace key pressed (and player isn't already jumping), push player
     if (IsGrounded(player) &&
         IsKeyPressed(KEY_SPACE))
     {