Merge branch 'ps/pseudo-ref-terminology' into ps/ref-storage-migration

* ps/pseudo-ref-terminology: refs: refuse to write pseudorefs ref-filter: properly distinuish pseudo and root refs refs: pseudorefs are no refs refs: classify HEAD as a root ref refs: do not check ref existence in `is_root_ref()` refs: rename `is_special_ref()` to `is_pseudo_ref()` refs: rename `is_pseudoref()` to `is_root_ref()` Documentation/glossary: define root refs as refs Documentation/glossary: clarify limitations of pseudorefs Documentation/glossary: redefine pseudorefs as special refs