Merge branch 'rh/ishes-doc'

We liberally use "committish" and "commit-ish" (and "treeish" and "tree-ish"); as these are non-words, let's unify these terms to their dashed form. More importantly, clarify the documentation on object peeling using these terms. * rh/ishes-doc: glossary: fix and clarify the definition of 'ref' revisions.txt: fix and clarify <rev>^{<type>} glossary: more precise definition of tree-ish (a.k.a. treeish) use 'commit-ish' instead of 'committish' use 'tree-ish' instead of 'treeish' glossary: define commit-ish (a.k.a. committish) glossary: mention 'treeish' as an alternative to 'tree-ish'