Feature: Add dimensions tracking

[petcupaula]

What

• Adds support for tracking dimensions (Matomo documentation on Custom Dimensions: https://matomo.org/faq/reporting-tools/create-track-and-manage-custom-dimensions/)
• As mentioned in Is it possible to track custom dimensions? #16, example use cases would be tracking of App Version or tracking of App Content Language.

Implementation considerations

• Basically the dimensions are key value pairs, so in the proposed implementation just adding them to the query params.
• There are two ways to add the dimensions, either when an event is tracked (and dimensions is an optional argument) via the updated trackEvent, or via a new function trackDimensions

Documentation

• Info on setting up custom dimensions on Matomo can be found here: https://matomo.org/faq/reporting-tools/create-track-and-manage-custom-dimensions/ and on the dimensions arguments in the API here: https://developer.matomo.org/api-reference/tracking-api
• Updated also the README file with usage examples

[TesteurManiak]

Everything seems good to me, thank you for your contribution @petcupaula
Your change will be part of the release 1.4.0