Remove the "make iwyu" build target. Move the functionality into the
recently introduced lint.fish script. Fix a lot, but not all, of the
include-what-you-use errors. Specifically, it fixes all of the IWYU errors
on my OS X server but only removes some of them on my Ubuntu 14.04 server.
Fixes#2957
Prior to this fix, read_ni would use parse_util_detect_errors
to lint the script to run, and then parser_t::eval() to execute it.
Both functions would parse the script into a parse tree. This allows
us to re-use the parse tree, improving perfomance.
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
