Add gyp file to generate build files for different build systems.

This allow one to build with their preferred build tool: ninja, make, xcode,
msvs.

The incantation to generate the build files is:
$ gyp --depth=. gumbo_parser.gyp

if you have gyp installed in your PATH.

Signed-off-by: Thiago Farina <tfarina@chromium.org>
fix copyright license
Merge pull request #38 from tfarina/gumbo-parser-gyp

Gumbo parser gyp