Pdf2bib

Main changes
- Added the CLI option -nostore, which allows the user to opt out of the default behaviour of pdf2doi regarding storing the found identifier into the pdf metadata. When -nostore is added to the CLI invokation of pdf2bib, the pdf files will not be modified by pdf2doi.

Added
- Make sure entry id can not contain commas https://github.com/MicheleCotrufo/pdf2bib/pull/8.
- Make sure that the input variable target is converted to a string before processing, and Fix trailing colon for some PDF files https://github.com/MicheleCotrufo/pdf2bib/pull/16.

-Fixed a bug that made it possible that the author string would end with a final "and"
-Reshaped the output when using it via command line

-Cleaned up code, removed several unused imports
-Fixed a bug in the bibtex_makers.make_bibtex(metadata) function

- Initial release
- BibTeX functionalities separated from the older version of pdf2doi (v0.7)