First pass of cynic-parser

[obmarg]

Why are we making this change?

There are parts of the latest spec that graphql-parser doesn't support, so I want to replace it with an alternative.

Other options out there that I'm aware of:

• async-graphql-parser would work but its AST is quite annoying to work with, and last time I tested it was slower than graphql-parser.
• apollo-parser continues on failure to parse, which is nice but means there are a lot of Options in its AST. I don't particularly want that behaviour so that's out.
• apollo-compiler would probably make apollo-parser workable, but feels like too heavy a dependency for my needs.

So it looks like I might write my own. Also, it'll be fun.

What effects does this change have?

Adds the first pass of a parser for GraphQL type system documents.

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