* add basic implementation for bookmark support.

basically, add a file named ~/.mu/bookmarks which looks something like
  ----
  [mu]
  testarch=subject:test maildir:/archive
  inbox=maildir:/inbox
  ----

  now, one can do a query, e.g.

    mu find -b testarch

  which is equivalend to

    mu find subject:test maildir:/archive

 if both a bookmark and a 'normal' search expression are specified,
 the will be concatenated.

 bookmarks starting with mu_ are reserved for mu itself.

src/mu-util.h

@@ -76,6 +76,23 @@ gchar* mu_util_guess_mu_homedir (void);
 gchar* mu_util_guess_xapian_dir (const gchar *muhome);
 
 
+/**
+ * guess the place of the bookmark file (typically,
+ * ~/.mu/bookmarks). Note that this does not mean the file actually
+ * exists.
+ * 
+ * @param muhome the mu home directory or NULL, in which the muhome
+ * directoy will be guessed as well
+ *  
+ * @return the guessed mu bookmark file, which needs to be freed with
+ * g_free when no longer needed.
+ */
+gchar* mu_util_guess_bookmark_file (const gchar *muhome);
+
+
+
+
+
 /**
  * if path exists, check that's a read/writeable dir; otherwise try to
  * create it (with perms 0700)
@@ -157,6 +174,9 @@ gchar* mu_util_str_from_strv (const gchar **params) G_GNUC_WARN_UNUSED_RESULT;
 #define MU_XAPIAN_DIR_NAME    "xapian"
 #define MU_XAPIAN_VERSION_KEY "db_version"
 
+/* name of the bookmark file */
+#define MU_BOOKMARK_FILENAME "bookmarks"
+
 /**
  * log something in the log file; note, we use G_LOG_LEVEL_INFO
  * for such messages