log: Support --key, as well as --branch and --unused

--all remains a special case, since it is more efficient and displays in a
nicer order.

Sponsored-by: the NIH-funded NICEMAN (ReproNim TR&D3) project

doc/git-annex-log.mdwn

@@ -38,6 +38,18 @@ false, information may not have been committed to the branch yet.
   In this mode, the names of files are not available and keys are displayed
   instead.
 
+* `--key=keyname`
+
+  Displays the location log for the specified key.
+
+* `--branch=ref`
+
+  Displays the location log for the files in the specified branch or treeish.
+
+* `--unused`
+
+  Displays the location log for files found by last run of git-annex unused.
+
 * `--sizesof=repository`
 
   Displays a history of the total size of the annexed files in a repository

doc/todo/add_--key_to___34__annex_log__34__.mdwn

@@ -13,3 +13,5 @@ In my case -- doing archaeology on AFNI's test data in [https://github.com/afni/
 
 [[!meta author=yoh]]
 [[!tag projects/repronim]]
+
+> [[done]] --[[Joey]]