Updated include-what-you-use to 0.7.

Set LICENSE.

wyu 0.7 compatible with llvm+clang 3.9 is released. Major changes:

    Add preliminary mappings for libc++.
    Require the complete type for pointer arithmetic.
    Recognize nested classes in friend declarations.
    Better handling of X-macros/textual includes.
    Better handling of self-checking private headers (that raise an #error if included directly).
    Improve IWYU's understanding of implicit include dirs; the current source file's dirname is always a candidate now.
    Add implicit include dirs for libc++ on Darwin targets.
    Lots of internal cleanup based on output from clang-tidy.
    Reduce logging strategically, to get more relevant output.

(wiz)