Update Readme.md

Fix broken links -- libpthread_workqueue, libkqueue and libBlocksRuntime have moved to Github.
Fix travis build config.

- Install newest CMake.
- Test build with both Clang and GCC.
- Test build with Make and Ninja.
Add shiny travis build status icon
Add clang-format configuration
Revert the C++ compatibility changes.

- These only make it harder to track the official Apple version at
  <opensource.apple.com>.
- Visual Studio 2013 supports C99 now
- For dispatch i/o, we could get GCC compatibility by compiling this
  file only as C++, and substituting C++11 lambdas for blocks with some
  preprocessor shenanigans. Or using Clang's libtooling to rewrite the
  source.
Rename some constants for cross-platform compat
Rename #define to match Mavericks source tree
Squash warnings about unused variables
Fix incompatibility between Clang and some variants of unistd.h

The presence of '__block' as a parameter name in unistd.h in some Glibc
releases caused Clang to issue a compiler error.
Simplify build system

- Remove automake build system -- I don't have the knowledge to maintain
  it.
- Remove Darwin-specific stuff from CMake build system -- this was
  pretty superfluous, and never tested.
- Combine the various CMake helper functions into a single file
- Remove CTest - it's not a particularly compelling tool.
Rename get_main_queue_eventfd to get_main_queue_handle