Optimize the encoding and decoding of UTF8 and US_ASCII.

The new implementations are faster then the one that is shipped with the JDK and also
produce less objects, which in fact means less objects to GC.
Handle as before
Use correct charset
Prefix with UTF8
Seems like it is faster to have optimized versions
Fix bug
Merge branches 'master' and 'write_charsequence' of https://github.com/fengjiachun/netty

Conflicts:
	buffer/src/main/java/io/netty/buffer/ByteBuf.java
	buffer/src/main/java/io/netty/buffer/ByteBufUtil.java
	buffer/src/main/java/io/netty/buffer/PooledHeapByteBuf.java
	buffer/src/main/java/io/netty/buffer/PooledUnsafeDirectByteBuf.java
	buffer/src/test/java/io/netty/buffer/AbstractByteBufTest.java
	codec-http/src/main/java/io/netty/handler/codec/http/HttpObjectEncoder.java
	pom.xml