Vue 3.x support

[psmyrek]

Suggested merge commit message (convention)

Feature: Added support for Vue 3.x. Closes #158.

Internal: Merged code coverage reports from test runs from both Vue versions before sending them to Coveralls. Closes #162.

BREAKING CHANGE: Now, the CKEditor is a function that accepts an object as its one and only argument with the version property. For Vue 3.x also the h function is required during initialization and it must be passed to this object argument.

BREAKING CHANGE: The prop name used by v-model directive has changed from value to model-value.

[coveralls]

Pull Request Test Coverage Report for Build 179

• 37 of 37 (100.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

---

Totals
Change from base Build 143:	0.0%
Covered Lines:	38
Relevant Lines:	38

---

💛 - Coveralls

[psmyrek]

There are some strange errors in CI build:

$ npm install
npm WARN checkPermissions Missing write access to /home/travis/build/ckeditor/ckeditor5-vue/node_modules/@vue/test-utils
npm WARN checkPermissions Missing write access to /home/travis/build/ckeditor/ckeditor5-vue/node_modules/vue
npm ERR! code ENOENT
npm ERR! syscall access
npm ERR! path /home/travis/build/ckeditor/ckeditor5-vue/node_modules/@vue/test-utils
npm ERR! errno -2
npm ERR! enoent ENOENT: no such file or directory, access '/home/travis/build/ckeditor/ckeditor5-vue/node_modules/@vue/test-utils'
npm ERR! enoent This is related to npm not being able to find a file.
npm ERR! enoent 

@pomek @oleq Have you ever seen them before?
Re-triggering build does not help 😞

[psmyrek]

The following things will have to be done before merging this PR:

• CI build is failing:

npm WARN checkPermissions Missing write access to /home/travis/build/ckeditor/ckeditor5-vue/node_modules/@vue/test-utils
npm WARN checkPermissions Missing write access to /home/travis/build/ckeditor/ckeditor5-vue/node_modules/vue

• Code coverage reports from both test runs (for Vue 2.x and Vue 3.x) should be merged together, because the component code targets both Vue versions - Merge code coverage reports from test runs from both Vue versions #162.

[oleq]

Everything looks good to me except for the "Executing tests" section of the README.md file. The configuration options listed there no longer make sense and some new scripts (like npm run coverage) were included so I think it's worth updating.

If bringing support for test watcher or reporter options is a big issue now, let's drop the support for these. We can always get back and implement them and they're not critical for a small project like this one.

[psmyrek]

README.md has been updated.

[psmyrek]

Closed as the proposal to re-use one codebase for both Vue versions is not ideal and requires some hacks to work properly.
New PR has been created: #165