With this 'txt' files are now read and written. However, they don't have
any metadata so they don't show up correctly in the sort order and
currently the Markdown Editor is still available for them.
Related to #55
Possible Options - modified, mod, lastModified, lastMod, lastmodified or
lastmod. When read the the note we will figure out which one is being
used and accordingly write back that value.
This makes it easier to use GitJournal for editing Hugo websites as they
usually use the 'lastmod' field to indicate when the post was last modified.