Adding initial cmake infrastructure.

Also, updating `abacus.h` to use package version from top-level
CMakeLists.txt.
Updating cmake infrastructure.

Updating `FindCheck.cmake` module and `test/CMakeLists.txt` to
successfully run a Check unit test. However, the current approach to get
this to work seems very hack-tacular.
Working on cmake set up.

Updating `FindCheck.cmake` module and the cmake infrastructure for
building and running tests.
Updating cmake processing of header file.
Adding `.gitignore` to `src` directory.

Telling git to ignore the `abacus_config.h` file generated
by cmake.
Updating top-level and test CMakeLists.txt files.

Adding cmake support for all check unit tests. Adding `CMakeLists.txt`
file to `test/data` directory, which copies the test data files required
for the tests to the binary directory.
Adding `FindGSL.cmake` to cmake modules.
Updating `test/CMakeLists.txt`

Adding support for tests that require gsl. The entire Check unit test
suite is now up and running (and passing) under cmake build.
Updating `FindGSL.cmake`

Better handling of check for gsl_cblas library.
Updating `src/CMakeLists.txt`.

Updating src cmake file to build all executables. As in the autotools
build, `dpdraw` is only built if GSL is found.
Removing check for `Threads` package in test cmake file.
Updating `src/CMakeLists.txt`.

Adding support for installing executables via `make install`.
Adding packaging to top-level cmake file.

Creating target "dist" to create a source tar ball.
Adding `build.sh`.

This shell script will be the main script for configuring, building, and
installing the package with cmake.
Updating `build.sh` help message.