Support new core functions

[Biont]

Please check if the PR fulfills these requirements

• [x] The commit message follows our guidelines
• [ ] Tests for the changes have been added (for bug fixes/features)
• [x] Docs have been added/updated (for bug fixes/features)

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...) Feature

What is the current behavior? (You can also link to an open issue here) A couple of cache-related core functions are not implemented, namely

• wp_cache_flush_runtime
• wp_cache_add_multiple
• wp_cache_set_multiple
• wp_cache_delete_multiple
• wp_cache_flush_group
• wp_cache_supports

What is the new behavior (if this is a feature change)?

The functions mentioned above are now implemented

Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?) There should not be a breaking change here, no

Other information: Adresses #28

[Biont]

Merging since the e2e-branch on top of it has been reviewed