added exclusions argument to string_keys
added keys_are_syms=true argument to self.nested_value_set
Merge pull request #48 from sholland/string_keys_exclusions

ZA-432: added exclusions argument to string_keys
Merge pull request #49 from sholland/conv_to_s_vs_sym_option

added keys_are_syms=true argument to self.nested_value_set