Added unit tests

Added unit tests using the Google Test library. The library libgtest.a is
included in this commit. It was built from the package gtest-1.7.0.
Changed SEq to SEq_hat

Because the result we access is a unit quaternion. The only time SEq_hat is
just SEq is when it has been integrated with SEq_dot and delta time in the
filter.
Fixed SEq not being SEq_hat

Just another fix.
Updated .gitignore

Changed how unit test outputs are ignored.
Got Google Test working

Fixed how libgtest.a is linked in the Makefile. Made a 'Hello World' type
main.cpp for testing that I can compile with Google Test now.