Add new introspectable Vlint library

[esodan]

This new library is introspectable, so it produce GIR/TYPELIB files to be used by JavaScript, Python and any other library introspectable depending on it.

These changes also fix memory leaks because when running checks for files it never removes created Vala.Context using pop() method.

[kgrubb]

@esodan aside from the build file conflict, this looks good to me!