Add a check-metadata command

[ClmntBcqt]

PR for issue #15

[lebouquetin]

For better extensibilité, the alogrithm should be exported into a reusable function.

Example:

for page in Page.load_glob(path = list(map(lambda p : Path(p).absolute(), options["content path"])), all = True) :
    metadata_status = get_metadata_status_for(page)
    self.stdout.write("{:3.0f}% : {}".format(
        metadata_status.complete_percent,
        page.path.relative_to(page.content_page_dir)
    )
    if not metadata_status.is_complete():
        print [...]

[lebouquetin]

I added a last suggested (but not required) improvment. You decide if you merge like this or if you implement the suggestion then merge.

[lebouquetin]

I suggest addind parenthesis for readability self.complete = (self.missing == []) and (self.empty == [])

For readability comparison:

self.complete = self.missing == [] and self.empty == []
self.complete = (self.missing == [] and self.empty == [])
self.complete = (self.missing == []) and (self.empty == [])

Note that in the second line, black will remove parenthesis

[lebouquetin]

According to the way you implement it, I suggest to rename get_metadata_status_for() to process()

So you use it like:

            metadata_status = MetadataStatus()
            metadata_status.process(page)

Another way would be to implement get_metadata_status_for() as a class method returning a MetadataStatus instance:

            metadata_status = MetadataStatus.get_metadata_status_for(page)

Note: this is not required for merge but it would make the code more readable for future maintainance

[lebouquetin]

The standard way to implement classmethod is:

  @classmethod
  def get_metadata_status_for(cls, page) :
    [...]