Use CharSequence instead of String in parseContent()

and parseContentDepth(). This also means that the type of some fields
changed from String to CharSequence.

Also add Matcher for CharSequences.
Remove Packet.ID_NOT_AVAILABLE
Do not hardcode the char[] length in StringUtils
Throw IllegalStateException in StringUtils.hash()

instead of Log.

Also create UTF8 and SHA1 constant.
Use XmlStringBuilder in RosterPacket and XMPPError
Fix TLSUtils.AcceptAllTrustManager

Should not throw an Exception, but instead return a zero-sized
array. Also add some javadoc.