Update File2Txt.py

* Used `os.path.splitext()` to remove `drop_extension()`.
* Exit if no filename is provided
* Exit if filename ends with .txt.
* Opened `in_file` first to ensure that creation of `out_file` was required.
* When using the syntax `with open()`, you should not call `close()` on those files.
*
Merge pull request #1 from cclauss/patch-1

Merge pull request for File2Txt.py from cclauss/patch-1