Vue 3 Support

[fm96-dev]

This PR adds the plugin's Vue 3 support + useShepherd() composable function for the usage in setup hooks.

To make that possible I use vue-demi library, but there are some limitations in terms of building the package.

In package.json's module field I have changed it to src/entry.js because vue-demi works at build time, so I remove the ESM compilation since it was unnecessary and user can directly use src/entry.js.

The problem is for the SSR and unpkg versions... I think that the solution can be to build two versions of each build type, where:
One will still support Vue 2 (files named vue2-shepherd.min.js & vue2-shepherd.ssr.js)
and the others for Vue 3 (files named vue3-shepherd.min.js & vue3.shepherd.ssr.js).

These changes are not in this commit, if you are ok with this solution I'll make the change.

[RobbieTheWagner]

@fech-dev thank you so much for the PR and sorry for the delay in responding! After thinking about it some more, I think I am okay with completely dropping Vue 2 support, so if you would like to proceed with updating to entirely Vue 3 and composables, I support that 👍

[fm96-dev]

@fech-dev thank you so much for the PR and sorry for the delay in responding! After thinking about it some more, I think I am okay with completely dropping Vue 2 support, so if you would like to proceed with updating to entirely Vue 3 and composables, I support that 👍

Thanks @rwwagner90. Ok, I'll try to update asap.

[RobbieTheWagner]

@fech-dev did you still want to update this PR?

[fm96-dev]

@fech-dev did you still want to update this PR?

Sorry, for the late reply, but I was very busy.
I've made a commit, let me know if it's ok.

[RobbieTheWagner]

@fech-dev do you mind rebasing this please?

[RobbieTheWagner]

@fech-dev thanks for all the hard work! Just released 2.0.0