Added option to use generics with the compile method

[Gamote]

I've added support for generics on the compile method in order to take advantage of the Typescript validation when we are defining the schema as a param.

Usage (before):

type LoginRequest = {
  email: string;
  password: string;
};

const v = new Validator();

type CValidationSchema<T = any> = {
  $$strict?: boolean | 'remove';
  $$root?: boolean;
} & {
  [key in keyof T]: ValidationRule | undefined | any;
}

type CValidator<T> = (value: T) => true | ValidationError[];

const typedCompiler = <T>(schema: CValidationSchema<T>): CValidator<T> =>
  v.compile(schema);

const loginRequestValidator = typedCompiler<LoginRequest>({
  email: {type: 'email'},
  password: {type: 'string', empty: false, min: 6},
});

Usage (after):

type LoginRequest = {
  email: string;
  password: string;
};

const v = new Validator();

const loginRequestValidator = v.compile<LoginRequest>({
  email: {type: 'email'},
  password: {type: 'string', empty: false, min: 6},
});

I've set the T default value to any so the compile method can still be used without generics.

The most concerning part for me, regarding this commit, is that I've changed the ValidationSchema from interface to type. I've checked the code and I couldn't find any possible issue with it but I'm not totally sure about all the consequence. So please let me know if you find something.

If everything it's alright, I will continue with other PRs.

[coveralls]

Coverage remained the same at 100.0% when pulling 3e5689d on Gamote:patch-1 into 22edf46 on icebob:master.

[erfanium]

🤔🤔🤔
Changes looks great to me. But I think extending the CheckerFunction It's not as complicated as you think. (To follow the principle of simplicity)

interface CustomCheck<T> {
   (schema: T): true | FV.ValidationError[]
}

interface Schema {
   name: string
}

const check: CustomCheck<Schema>  = validatorBase.compile({
   name: 'string'
})