Introduce 'kotlin' script for running programs

'kotlin' is to 'kotlinc' what 'java' is to 'javac'. However it will support
much more: running class by name, jar, scripts, expressions, REPL

compiler/cli/bin/kotlinc-js.bat

@@ -14,6 +14,7 @@ rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 rem See the License for the specific language governing permissions and
 rem limitations under the License.
 
-set KOTLIN_COMPILER=org.jetbrains.kotlin.cli.js.K2JSCompiler
+setlocal
+set _KOTLIN_COMPILER=org.jetbrains.kotlin.cli.js.K2JSCompiler
 
 call %~dps0kotlinc.bat %*