Renamed CloudJS::string() to CloudJS::getString() to avoid Ubuntu GCC build issue

This will fix #41 issue.
I tried to replace CloudJS.hpp - `string string(){` to `::string string(){` and `std::string string(){`,
but both didn't fix the issue.
I found the following site, and this seems to be GCC specific issue.
http://stackoverflow.com/questions/12943607/can-a-member-of-a-class-be-named-the-same-name-as-its-type-another-class
So, I replaced `string string(){` to `string getString(){`.
If there is no strong reason to use `string string(){`, I think that this way is the easiest one to fix the issue.