Add object iterator for environment objects

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

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Move sexpr to util directory

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add initializer list constructor for hierarchical names

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add pretty printer for s-expressions and options

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add static_asserts for higher-order functions in kernel/for_each.h and kernel/pp.cpp
Fix typos in format.h (error messages)
Add more to mpfp