Expand ComicInfo support and add support for comic covers

[carif]

This change adds support for ComicInfo metadata stored within the comic itself. While implementing this, we decided to take a look at the existing provider which reads ComicInfo metadata stored outside the comic. Both cases now use a common class to read the ComicInfo format. More tags than previously are now supported. We can however not guarantee that this covers all possible tags supported by the ComicInfo format. Covers of comics are read now.

Changes

• Add an interface for Comic metadata from files. This interface is implemented by all files which read in metadata and the provider serves as a proxy. External metadata is read in first, internal metadata is read in if no external metadata is found.
• As this change adds support for internal metadata, a general class got added which provides methods to read in the ComicInfo format. This class is used by the internal provider, but also by the external provider.
• Expand the number of supported tags for the ComicInfo format.
• Add an image provider for comics.
• Clarify which comic metadata formats are supported in the README.md file.

Limitations

• No support for other formats than CBZ. However, if the metadata is stored externally, it can still be read.
• The algorithm to search for covers is very simplistic and can be made more intelligent. For example, certain metadata formats like the "Advanced Comic Book Format" may store additional information to help identify the cover within the comic.

What this PR does NOT

• Add test cases for this project. However, we tried to design our classes in a way which hopefully makes it easy to add test cases to them.
• Add support for the "ComicBookInfo" and "Advanced Comic Book Format".

Issues

Fixes #18

[carif]

Quick first pass

I may have missed some log lines, so here's the summary of the log change

* Logs shouldn't use string interpolation

* Logs shouldn't end in a full stop (`.`)

Seems like you got all log lines xD