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
fix muls and divs for new group/groups
big endian support for group
remove references to unused 'load' function in group test
int8/16 sse2 implementation must use divs+groups. A better implementation should be possible.
add type complex groups unit test
use groups-based implementation of muls except for ints32 on sse and avx which uses group