This change moves source files into a src/ directory,
and puts object files into an obj/ directory. The Makefile
and xcode project are updated accordingly.
Fixes#1866
Fixes a bug where generating a lot of autoloaded functions from
syntax highlighting would result in evicting nodes on background threads,
resulting in a thread error.
Fixes#1989
history_lru_node_t has implicit destructor defined. However, because
it's being deleted as lru_node_t, it's not being actually called, as
lru_node_t doesn't have a virtual destructor.
