Fix unity project folder.

This commit also rename assets directory to asset directory to avoid troubles
of Unity Editor which attempts to open source root instead of project folder
because of existent of the assets folder.

Author: yfakariya

assets/Big.png asset/Big.pngassets/Big.png renamed to asset/Big.png

@@ -1,21 +1,28 @@
-/[Aa]ssets/
 /[Ll]ibrary/
 /[Tt]emp/
 /[Oo]bj/
 /[Bb]uild/
 /[Bb]uilds/
+/Assets/AssetStoreTools*
+/UnityPackageManager/
+
+# Visual Studio 2015 cache directory
+/.vs/
 
 # Autogenerated VS/MD solution and project files
 ExportedObj/
+.consulo/
+*.csproj
 *.unityproj
+*.sln
 *.suo
 *.tmp
 *.user
 *.userprefs
 *.pidb
 *.booproj
 *.svd
-
+*.pdb
 
 # Unity3D generated meta files
 *.pidb.meta
@@ -27,4 +34,5 @@ sysinfo.txt
 *.apk
 *.unitypackage
 
-/[Aa]ssets/[Pp]lugins/[Dd]lls/
+# Assets except .gitkeep should not be committed in this project.
+/[Aa]ssets/