feat(kernel/abstract): add more Pi functions for simplifying the creation Pi-expressions

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(kernel/expr): add additional template for mk_app

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(util/name): add methods append_after and append_before

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(kernel/formatter): avoid hierarchical names when printing local constants

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
test(lua): fix n6.lua, and add more tests

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(kernel/inductive): add eliminator/recursor for inductive datatype declarations

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>