Reimplemented CharacterDetector in more modular way.
Override UTF-16 charsets in META tag as prescribed by WHAT-NG.
Add BOM sniffer.
Also includes CompositeResource for representing revisited resource as single Resource (not for general use yet).
Addresses ARI-3933.
BUGFIX: StandardCharsetDetector must not return null.
(also added javadoc note of the requirement)
add a test for ContentTypeHeaderSniffer.
TEST: add tests for TimeMapRequestParser.
  it reveals a few inconsistent/surprising behaviors
Merge branch 'ARI-3933'