added to_s()
added boolean.h
added util.{h,cpp}
added pair.{h,cpp}
added cons(), car(), ...
added empty.h
changed namespace: booscheme -> boo
added new files
added number.cpp, symbol.cpp and environment.cpp
updated boo.h and boo.cpp
remove unnecessary code
remove unnecessary code
remove unnecessary code
remove unnecessary code
remove boost::any
updated