Honor target attribute for outbound link tracking by relying on navigator.sendBeacon

[suabahasa]

Description

Continue the effort from the PR #45.
The outbound link tracking event is sent with navigator.sendBeacon to honor the target attribute for outbound link tracking.

uBlock Origin prevents ping requests with navigator.sendBeacon when the "Disable hyperlink auditing" option is enabled https://github.com/gorhill/uBlock/wiki/Dashboard:-Settings#disable-hyperlink-auditing

Related Issue

Fixes #12
Implement #16

Screenshots or GIFs (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.