rename group to groups, introduce new function group
generalize deinterleave_first implementation to all integers
add complex group
add groups tests and benchmarks as copies from their respective group equivalents
add NT2_TEST_CASE_TPL_MPL and NT2_TEST_SEQ_MPL_FILTER macros to be able to define tests on a set of types that satisfy a given predicate.
use new NT2_TEST_CASE_TPL_MPL macro to fix group test and add special cases for floating-point or not