removed bin/ folder which was not used anyway
moved legacy PHP code into php/ directory

Since the C++ rewrite is coming along pretty nicely, that source
base will become the "official" version of the compiler. The PHP
code should stick around for some time though, since it might
contain some hints as to how certain things might be implemented;
especially since a form of type inference was already present there.
moved cpp/ to the project root

Also added runc.sh which compiles a Maxwell file to an
executable in one go by parsing it, feeding it through
the compiler stages, packaging it as C source files and
running them through gcc.
fixed runc and finalize restructuring for cpp

Closes issue #1. There's still some more refactoring required to
make things easier to navigate. concept/ and language/ should be
merged to a certain extent, and specs/ should be moved into language/.
restructured language documents

Renamed `concept` directory to `language`, and the former  `language`
directory to `language/samples`. Also renamed `specs` to `language/editor-support`.