COPYING: replace BSD-3-Clause by Apache-2.0

The only source file (src/main.c) contains an Apache-2.0 header so copy
this header in COPYING instead of the BSD-3-Clause license text.
For more information, see:
#2

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>

COPYING

@@ -1,23 +1,13 @@
- Copyright 2008, The Android Open Source Project
+ Copyright (C) 2009-2011 Broadcom Corporation
 
- Redistribution and use in source and binary forms, with or without
- modification, are permitted provided that the following conditions are met:
-     * Redistributions of source code must retain the above copyright
-       notice, this list of conditions and the following disclaimer.
-     * Redistributions in binary form must reproduce the above copyright
-       notice, this list of conditions and the following disclaimer in the
-       documentation and/or other materials provided with the distribution.
-     * Neither the name of Google Inc. nor the names of its contributors may
-       be used to endorse or promote products derived from this software
-       without specific prior written permission.
+ Licensed under the Apache License, Version 2.0 (the "License");
+ you may not use this file except in compliance with the License.
+ You may obtain a copy of the License at
 
- THIS SOFTWARE IS PROVIDED BY Google Inc. ``AS IS'' AND ANY EXPRESS OR 
- IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
- MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO 
- EVENT SHALL Google Inc. BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
- SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
- PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; 
- OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 
- WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR 
- OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
- ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+     http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.