binary_heap: rename move_down/move_up to sift_down/sift_up

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
documentation: add guidelines for naming data structure functions

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
binary_heap: add Wikipedia links

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
tests: add TEST_INT_IS_GREATER_THAN_OR_EQUAL macro

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
tests: add more tests for binary heap

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>