Add basic support for index types and imports

[pzavolinsky]

Support parsing TS index types, e.g.:

interface A { b: { c: string; } }
interface B { ref: A['b'] }

produces:

export const A = {
  b: {
    c: 'string',
  },
};

export const B = {
  ref: A.b,
};

Support (basic) imports, e.g.:

import { SomeType } from './file';
interface A {
  x: SomeType;
}

when run with -i './file', produces:

import { SomeType } from './file';
export const A = {
  x: SomeType,
};

and when run with -i './file:../path/to/generated/schemas/file', produces:

import { SomeType } from '../path/to/generated/schemas/file';
export const A = {
  x: SomeType,
};