New rule: skipLibCheck must be false

[danielnixon]

This can save time during compilation at the expense of type-system accuracy.

https://www.typescriptlang.org/tsconfig/skipLibCheck.html

[danielnixon]

https://github.com/fp-ts/schema is going to require exactOptionalPropertyTypes, so let's add a rule for that too

[danielnixon]

Hmmm:

typings/typescript.d.ts:8:14 - error TS2687: All declarations of 'isArrayType' must have identical modifiers.

8     readonly isArrayType: (type: Type) => type is TypeReference;
               ~~~~~~~~~~~

typings/typescript.d.ts:8:14 - error TS2717: Subsequent property declarations must have the same type.  Property 'isArrayType' must be of type '(type: Type) => boolean', but here has type '(type: Type) => type is TypeReference'.

8     readonly isArrayType: (type: Type) => type is TypeReference;
               ~~~~~~~~~~~