Fix incorrect type-declaration

[manuth]

General

The front-matter module uses the module.exports = fm-pattern to expose the library.
Currently the type-declaration doesn't represent this correctly and instead asserts an export default fm.

This contradicts with each other and causes typescript to not work correctly.

This PR fixes the type-declarations accordingly.

The Solution

The solution is to move every existing component (such as FrontMatterOptions, FM etc.) into a namespace which merges with the fm-function:

front-matter/index.d.ts

Lines 1 to 23 in d367565

	declare namespace fm {
	export interface FrontMatterResult<T> {
	readonly attributes: T
	readonly body: string
	readonly bodyBegin: number;
	readonly frontmatter?: string
	}
	export interface FrontMatterOptions {
	/**
	* Whether to use [safeload](https://github.com/nodeca/js-yaml#safeload-string---options-)
	* @default true
	*/
	allowUnsafe?: boolean
	}
	export interface FrontMatter {
	<T>(file: string, options?: FrontMatterOptions): FrontMatterResult<T>
	test(file: string): boolean
	}
	}
	declare const fm: fm.FrontMatter;

Afterwards the fm-function can be exported the same way it is exported in the actual source-file (which is using an export = fm-expression):

front-matter/index.d.ts

Line 24 in d367565

export = fm;

Merging this PR fixes issue #76

[karlhorky]

@jxson @peterbe @tyankatsu0105 what do you think about this PR?

It looks like the current TypeScript types are broken:

• https://arethetypeswrong.github.io/?p=front-matter%404.0.2