feat: Support string concatenation using '#'

[emon100]

Modified Parser.js to support string concatenation using '#' mentioned in bibtex.

Example:

 a.bib: @proceedings{book, month = "4 " # jan # {--} # "6 " # dec, year = "2019" }

- Before
 ->a.json:  [{"ObjectType":"entry","EntryType":"proceedings","EntryKey":"book","Fields":{"month":"4"}}]

- After
 ->a.json:  [{"ObjectType":"entry","EntryType":"proceedings","EntryKey":"book","Fields":{"month":"4 January--6 December","year":"2019"}}]

Passed all 8 tests. Added a new test.

Also, removed two temp files.