Add convenience overload Appender::addFilter(std::function<..>).
patternlayout.cxx: Modernize C++.

Use some C++11 loops. Use std::unique_ptr<>. Replace string's `substr()` with
`assign()` calls.
Remove logloguser.{h,cxx} as their are completely unused.
configurator.cxx: Use lambda instead of `bind1st()`, etc.
More C++11 related tweaks.
Make AbstractSocket, etc., movable-only type.
Move iOS related note from iOS/README.txt to README.md.
property.cxx: Modernize C++.
loglevel.cxx: One more C++11 for(a:b) loop.
logleve.{h,cxx}: Modernize C++.
loggingserver.cxx: Fix variable shadowing warning.
Modernize C++11. Use few more nullptrs and for(a:b) loops.
Start new ChangeLog for 2.0.
.travis.yml: Try to fix Travis CI builds by using Clang 3.5.
.travis.yml: Try another fix for Clang installation on Travis CI.
.travis.yml: Re-enable Clang testing.
Revert ".travis.yml: Re-enable Clang testing."

This reverts commit 4fdfe093a58a6b2c536d31301f0124b74ff3ee29.
Merge pull request #32 from wilx/master

Merge C++11 changes.