feat: Scan files from a directory

[mgmacias95]

closes #54 (comment)

[plusvic]

The code looks good to me, but the documentation for the command is still vt scan file [file].. which suggests that the only thing that it accepts is a list of files. We should reflect the new use case in the documentation. The usage line may be something like vt scan file [[dir] | [file]..], and we need to change the description as well, which currently says:

Scan one or more files.

This command receives one or more file paths and uploads them to VirusTotal for
scanning....

[mgmacias95]

PTAL