remove py2 remnants and use mocks in tests

fstring wip
Run pyupgrade
fix broken pyupgrade fstring
run pyupgrade on plugin dir
fixup! remove py2 remnants and use mocks in tests
small print bugfix
The file=sys.stderr was part of the format(), so an error got printed to
stdout
Drop use of codecs package
Use builtins.open() instead
fixup! remove py2 remnants and use mocks in tests

jrnl/DayOneJournal.py

@@ -1,7 +1,5 @@
 #!/usr/bin/env python
-# encoding: utf-8
 
-from __future__ import absolute_import, unicode_literals
 from . import Entry
 from . import Journal
 from . import time as jrnl_time
@@ -26,7 +24,7 @@ class DayOne(Journal.Journal):
     def __init__(self, **kwargs):
         self.entries = []
         self._deleted_entries = []
-        super(DayOne, self).__init__(**kwargs)
+        super().__init__(**kwargs)
 
     def open(self):
         filenames = [os.path.join(self.config['journal'], "entries", f) for f in os.listdir(os.path.join(self.config['journal'], "entries"))]
@@ -83,7 +81,7 @@ class DayOne(Journal.Journal):
     def editable_str(self):
         """Turns the journal into a string of entries that can be edited
         manually and later be parsed with eslf.parse_editable_str."""
-        return "\n".join(["# {0}\n{1}".format(e.uuid, e.__unicode__()) for e in self.entries])
+        return "\n".join([f"# {e.uuid}\n{str(e)}" for e in self.entries])
 
     def parse_editable_str(self, edited):
         """Parses the output of self.editable_str and updates its entries."""
@@ -107,7 +105,7 @@ class DayOne(Journal.Journal):
                 current_entry.modified = False
                 current_entry.uuid = m.group(1).lower()
             else:
-                date_blob_re = re.compile("^\[[^\\]]+\] ")
+                date_blob_re = re.compile("^\\[[^\\]]+\\] ")
                 date_blob = date_blob_re.findall(line)
                 if date_blob:
                     date_blob = date_blob[0]