Notes API: get_commit_notes() -> format_note() + remove the commit restriction

There is really no reason why only commit objects can be annotated. By
changing the struct commit parameter to get_commit_notes() into a sha1 we
gain the ability to annotate any object type. To reflect this in the function
naming as well, we rename get_commit_notes() to format_note().

This patch also fixes comments and variable names throughout notes.c as a
consequence of the removal of the unnecessary 'commit' restriction.

Signed-off-by: Johan Herland <johan@herland.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

notes.h

@@ -4,10 +4,19 @@
 /* Free (and de-initialize) the internal notes tree structure */
 void free_notes(void);
 
+/* Flags controlling how notes are formatted */
 #define NOTES_SHOW_HEADER 1
 #define NOTES_INDENT 2
 
-void get_commit_notes(const struct commit *commit, struct strbuf *sb,
+/*
+ * Fill the given strbuf with the notes associated with the given object.
+ *
+ * If the internal notes structure is not initialized, it will be auto-
+ * initialized to the default value (see documentation for init_notes() above).
+ *
+ * 'flags' is a bitwise combination of the above formatting flags.
+ */
+void format_note(const unsigned char *object_sha1, struct strbuf *sb,
 		const char *output_encoding, int flags);
 
 #endif