Merge pull request #11 from Codiferous/master

PULL: Add Clang Makefile and update GCC Makefile.
Move from vector::emplace_back to vector::push_back to fix cross-platform issues.
Update vcxproj to behave better with copy commands.
Remove unnecessary function StackElement::CopyObj.
Update README.md
Enable simple REPL for POSIX systems with GNU readline