V1.4: Added customization options.

You can now customize org-journal-file-name if you want to save your
files in a format other than YYYYMMDD. Be sure to update
org-journal-file-pattern to match those file names or the calendar
won't highlight journal entries and journal files won't be opened with
org-journal-mode by default.

You can now customize org-journal-date-prefix and
org-journal-time-prefix if you don't want journal entries to be org
headings and sub-headings. For example, you could set
org-journal-date-prefix to `#+TITLE:` in order to have every journal
file start with an org title.

Also made org-mode check the whole file path when deciding whether to
open a file in org-journal-mode.

Also limited line length to 80 characters.