fix #2: 'DefMacroMap [v] lhs rhs' does not expand mapmode-[xs] mappings

Code:
    DefMacroMap [v] lhs rhs
    " The following lhs-es are assumed '<lhs>' not 'rhs'.
    Map [x] <lhs> ...
    Map [s] <lhs> ...
s:expand_mode_chars() should not remove invalid chars silently
remove s:get_each_modes(), use s:expand_mode_chars() instead