cmake: add a project

Basically ensure C is enabled. Also disables C++ which isn't necessary
here.
cmake: use string(TIMESTAMP) instead of exec'ing date

Available since 2.8.11, so it's fine.
cmake: simplify if expressions

So CMake's if command has some weird behaviors which are warned about
now in 3.0. Avoid these warnings. Also replace a MATCHES with STREQUAL
because it's faster and there are no variants on the Ninja generator.
cmake: use @var@ replacement in configured files

Allows actual use of ${var} in the resulting files to be deferred to
execution time.
cmake: be explicit about include paths

We don't want to pick up other rogue files laying around for whatever
reason.
README: add ragel to the builddep list

Required for harfbuzz.
Merge pull request #14 from mathstuf/cmake-cleanups

CMake cleanups