Make TippyDirective extendable

[hagenstrahl]

I would like to extend from TippyDirective to add some custom behavior and keep the overall api the directive provides.

Sadly right now it's not extendable because of some missing types which are not exported in public api and accessing some properties is unintended because they are private.

My idea is:

• add TIPPY_CONFIG InjectionToken and TippyConfig to public api (https://github.com/ngneat/helipopper/blob/0c30ffbb49e1339578964018cad2800e587e1857/projects/ngneat/helipopper/src/lib/tippy.types.ts)
• make any private property and method in TippyDirective protected (https://github.com/ngneat/helipopper/blob/master/projects/ngneat/helipopper/src/lib/tippy.directive.ts)

What do you think?

[NetanelBasal]

You're welcome to submit a PR