Add API to generate automatic timestamp tag

The format is: YYYYMonDD
where,
  YYYY - numeric year
  Mon  - month string
  DD   - numeric day of month

While importing bookmarks, this tag will be added and reported to user if
`--tacit` option is not specified.

buku.1

@@ -77,6 +77,7 @@ Bookmarks with immutable titles are listed with '(L)' after the title.
   - Auto-import looks in the default installation path and default user profile.
   - URLs starting with `place:`, `file://` and `apt:` are ignored during import.
   - Folder names are automatically imported as tags if --tacit is used.
+  - An auto-generated tag in the format 'YYYYMonDD' is added if --tacit is not used.
 .PP
 .IP 10. 4
 \fBEncryption\fR is optional and manual. AES256 algorithm is used. To use encryption, the database file should be unlocked (-k) before using \fBbuku\fR and locked (-l) afterwards. Between these 2 operations, the database file lies unencrypted on the disk, and NOT in memory. Also, note that the database file is \fBunencrypted on creation\fR.

buku.py

@@ -34,6 +34,7 @@ import signal
 import sqlite3
 import sys
 import threading
+import time
 import urllib3
 from urllib3.util import parse_url, make_headers
 import webbrowser
@@ -1934,8 +1935,6 @@ class BukuDb:
             True on success, False on failure.
         """
 
-        import time
-
         count = 0
         timestamp = str(int(time.time()))
         arguments = []
@@ -2165,7 +2164,9 @@ class BukuDb:
             Path to file to import.
         tacit : bool, optional
             If True, no questions asked and folder names are automatically
-            imported as tags. Default is False.
+            imported as tags from bookmarks html.
+            If True, automatic timestamp tag is NOT added.
+            Default is False.
 
         Returns
         -------
@@ -2174,7 +2175,7 @@ class BukuDb:
         """
 
         if not tacit:
-            newtag = input('Specify unique tag for imports (Enter to skip): ')
+            newtag = gen_auto_tag()
         else:
             newtag = None
 
@@ -2207,6 +2208,9 @@ class BukuDb:
             self.conn.commit()
             infp.close()
 
+        if newtag:
+            print('\nAuto-generated tag: %s' % newtag)
+
         return True
 
     def mergedb(self, path):
@@ -2815,6 +2819,21 @@ def prep_tag_search(tags):
     return tags, search_operator, excluded_tags
 
 
+def gen_auto_tag():
+    """Generate a tag in Year-Month-Date format
+
+    Returns
+    -------
+    str
+        New tag as YYYYMonDD
+    """
+
+    import calendar as cal
+
+    t = time.localtime()
+    return ('%d%s%02d' % (t.tm_year, cal.month_abbr[t.tm_mon], t.tm_mday))
+
+
 def edit_at_prompt(obj, nav):
     """Edit and add or update a bookmark.