Add Apache License 2.0

Some files are licensed under Apache Software License 2.0. Clause 4(a) of this license says that any other recipients of the Work or Derivative Works must be given a copy of this License. Please consider adding this license text to the repository.

Thanks

List of files under ASL 2.0:
./src/main/java/hudson/remoting/Base64.java
./src/main/java/hudson/remoting/FastPipedInputStream.java
./src/main/java/hudson/remoting/TeeOutputStream.java
./src/main/java/hudson/remoting/FastPipedOutputStream.java