refactor(library/arith): move real and special function declarations to .lean files

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(library/io_state): move to the kernel

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(library/arith): do not load specialfn by default

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(builtin/basic): rename basic.lean to kernel.lean

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(kernel/builtin): move helper decl macros to a separate file

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
chore(*): cleanup builtin registration

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
chore(builtin): cleanup dependencies

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(builtin): only load the kernel and natural numbers by default

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
chore(library/all): remove unnecessary files

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