Eml-analyzer

- fixed encoding issue of payload with Transfer-Encodings ``7bit``, ``8bit``, ``binary``
- header value fields are now decoded
- For example: ``Subject: =?UTF-8?Q?Dies_ist_ein_d=c3=a4mlicher_Test?=``
- is now decoded to ``Subject: Dies_ist_ein_dämlicher_Test``
- input files are now explicity parsed as UTF-8

Fixes issue https://github.com/wahlflo/eml_analyzer/issues/14

- improved file name decoding by making it more flexible to support not only utf-8 encodings (Thanks to Favaloro)

- added unit test GitHub action workflow

- improved detection of URLs in HTML part
- improved decoding (URL & HTML decoding of detected URLs)
- changed typing annotations to ensure backwards compatibility to 3.7

- Complete Refactoring of the old code base to make it more readable and maintainable
- Intoduced unit tests & Makefile
- Extracted URLs are no longer limited only to HTML href tags. Now, also URLs like https://www.facebook.de/abc123 will be detected in paragraphs of the HTML or in the text part of the email. URLs without a protocol like facebook.de are still not detected, since this would probably lead to too many false positives. Also, the email clients I tried (e.g. Outlook) does not make these URLs clickable for the user.
- Now, there is the possibility to define a structured output (currently only JSON is supported) but it is easy to add more in the future if needed

- Standard input is now supported