Move strftime to util.date module

In this patch strftime function is moved out of main __init__.py module
to util.date, where it belongs.

ebook_converter/ebooks/conversion/plumber.py

@@ -14,8 +14,8 @@ from ebook_converter.ebooks.conversion.preprocess import HTMLPreProcessor
 from ebook_converter.ptempfile import PersistentTemporaryDirectory
 from ebook_converter.utils.date import parse_date
 from ebook_converter.utils.zipfile import ZipFile
-from ebook_converter import extract, walk, filesystem_encoding
-from ebook_converter.constants_old import __version__
+from ebook_converter import extract, walk
+from ebook_converter.constants_old import __version__, filesystem_encoding
 
 
 DEBUG_README=b'''

ebook_converter/ebooks/lrf/html/convert_from.py

@@ -20,10 +20,10 @@ from math import ceil, floor
 
 import bs4
 
-from ebook_converter import (
-    __appname__, entity_to_unicode, fit_image, force_unicode, preferred_encoding
-)
-from ebook_converter.constants_old import filesystem_encoding
+from ebook_converter import __appname__, entity_to_unicode, fit_image, \
+        force_unicode
+from ebook_converter.constants_old import filesystem_encoding, \
+        preferred_encoding
 from ebook_converter.devices.interface import DevicePlugin as Device
 from ebook_converter.ebooks import ConversionError
 from ebook_converter.ebooks.BeautifulSoup import html5_parser

ebook_converter/ebooks/oeb/transforms/jacket.py

@@ -8,12 +8,11 @@ import urllib.parse
 from xml.sax import saxutils
 
 from ebook_converter import constants as const
-from ebook_converter import strftime
+from ebook_converter.utils import date
 from ebook_converter.constants_old import iswindows
 from ebook_converter.ebooks.oeb import base
 from ebook_converter.ebooks.oeb.base import XPath, xml2text, urlnormalize
 from ebook_converter.library.comments import comments_to_html, markdown
-from ebook_converter.utils.date import is_date_undefined, as_local_time
 from ebook_converter.ebooks.chardet import strip_encoding_declarations
 from ebook_converter.ebooks.metadata import fmt_sidx, rating_to_stars
 
@@ -272,11 +271,11 @@ def render_jacket(mi, output_profile, alt_title='Unknown', alt_tags=[],
     publisher = saxutils.escape(publisher)
 
     try:
-        if is_date_undefined(mi.pubdate):
+        if date.is_date_undefined(mi.pubdate):
             pubdate = ''
         else:
-            dt = as_local_time(mi.pubdate)
-            pubdate = strftime('%Y', dt.timetuple())
+            dt = date.as_local_time(mi.pubdate)
+            pubdate = date.strftime('%Y', dt.timetuple())
     except Exception:
         pubdate = ''