Update type definitions to include custom export

[fredrikekelund]

Q	A
Bug fix?	yes
New feature?	no
BC breaks?	no
Deprecations?	no
Tests pass?	yes
Fixed tickets	N/A
License	MIT
Doc PR	N/A

Tip

Exclude whitespace changes when looking at the PR diff to see that I haven't actually changed all that much.

pm2 exports two members in the programmatic interface: default (an instance of API) and custom (the API class). However, the custom prop is not included in types/index.d.ts.

This PR fixes that problem by moving all function definitions inside an API class in types/index.d.ts. We then use this single definition to declare both the default and custom exports.

I also took the opportunity to update the start type definitions to take an ErrProcsCallback as the second parameter (a callback where the second argument is Proc[] instead of Proc).

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[fredrikekelund]

Several parts of this diff are just auto-formatting. This is one example.