Naive implementation of Python standard library's fileinput.input()

* fileinput.input() allow the sequential reading of file(s) whose path(s) were given as command-line arguments
* Failing to supply command-line arguments, the stdin is used to query user for path(s)
* Naive implementation, i.e. no support for original version's flags/options/keyword parameters
* Modification over original: verify supplied path is of a VALID file or ignore; when in interactive mode, empty line terminates user's input