[api-xml-adjuster] Set $(OutputPath) to $prefix/lib/mandroid (#27)

Change $(OutputPath) for api-xml-adjuster.csproj to be
bin/$(Configuration)/lib/mandroid instead of bin/$(Configuration).

This is more in keeping with the Xamarin.Android install structure.

tools/api-xml-adjuster/api-xml-adjuster.csproj

@@ -13,7 +13,7 @@
     <DebugSymbols>true</DebugSymbols>
     <DebugType>full</DebugType>
     <Optimize>false</Optimize>
-    <OutputPath>..\..\bin\Debug</OutputPath>
+    <OutputPath>..\..\bin\Debug\lib\mandroid</OutputPath>
     <DefineConstants>DEBUG;</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
@@ -22,7 +22,7 @@
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
     <Optimize>true</Optimize>
-    <OutputPath>..\..\bin\Release</OutputPath>
+    <OutputPath>..\..\bin\Release\lib\mandroid</OutputPath>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
     <ExternalConsole>true</ExternalConsole>