Add custom lint rule about import

[nadongguri]

I wanted to pretend package-private feature in this project.
In order to do that, adding tslint custom rule prevents the case when
ts file tries to import other modules in another folder except index.ts.

ISSUE=#231

[nadongguri]

$ ./bacardi lint_ts

[23:05:28] Requiring external module ts-node/register
[23:05:29] Using gulpfile ~/Desktop/lunchclass/bacardi/gulpfile.ts
[23:05:29] Starting 'lint_ts'...
/home/ryan/Desktop/lunchclass/bacardi/core/index.ts
should not import sub modules in other folder (no-import-other-modules)
18 | import {DefinitionInfo} from 'core/parser/idl_types';
19 | import {Parser} from 'core/parser/parser';

20 | import * as file from 'generator/base/file';
21 |
22 | async function readAndParse(idlFilePath: string): Promise {
23 | const idlFragment: string = await file.read(idlFilePath);

[23:05:33] 'lint_ts' errored after 3.67 s
[23:05:33] Error in plugin 'gulp-tslint'
Message:
Failed to lint: 1 errors.