Add Meson and Ninja syntax highlighting

[sorairolake]

Syntax:

• Meson: a general-purpose build system
• Ninja: a small build system that is the backend of Meson and GN (see: List of generators producing ninja build files)

Guideline Criteria:

• https://atom.io/packages/language-meson
• https://packagecontrol.io/packages/Ninja

I think it would be useful to support the syntax highlighting of these, because they are used in many famous software projects.

[sharkdp]

Thank you for your feedback. Sounds good to me!

[sharkdp]

Ninja is now included. I couldn't really find a sublime syntax for Meson. Closing this for now, unless someone has a Meson syntax.

[nullhook]

I'm not sure if this works for .gn files or there's partial support if I enforce -l ninja flag.