title: how to set main class in SBT 0.13 project
body: <p>Could you guys please explain to me how to set main class in SBT project ? I'm trying to use version 0.13.</p>
  
  <p>My directory structure is very simple (unlike SBT's documentation). In the root folder I have <code>build.sbt</code> with following content</p>
  
  <pre><code>name := "sbt_test"
  
  version := "1.0"
  
  scalaVersion := "2.10.1-local"
  
  autoScalaLibrary := false
  
  scalaHome := Some(file("/Program Files (x86)/scala/"))
  
  mainClass := Some("Hi")
  
  libraryDependencies ++= Seq(
      "org.scalatest" % "scalatest_2.10" % "2.0.M5b" % "test"
  )
  
  EclipseKeys.withSource := true
  </code></pre>
  
  <p>And I have subfolder <code>project</code> with single file <code>Hi.scala</code> which contains following code</p>
  
  <pre><code>object Hi {
    def main(args: Array[String]) = println("Hi!")
  }
  </code></pre>
  
  <p>I'm able to compile it by calling <code>sbt compile</code> but <code>sbt run</code> returns</p>
  
  <pre><code>The system cannot find the file C:\work\externals\sbt\bin\sbtconfig.txt.
  [info] Loading project definition from C:\work\test_projects\sbt_test\project
  [info] Set current project to sbt_test (in build file:/C:/work/test_projects/sbt_test/)
  java.lang.RuntimeException: No main class detected.
          at scala.sys.package$.error(package.scala:27)
  [trace] Stack trace suppressed: run last compile:run for the full output.
  [error] (compile:run) No main class detected.
  [error] Total time: 0 s, completed Apr 8, 2013 6:14:41 PM
  </code></pre>