allow user-defined output filename suffix

[mattsb42-aws]

Default behavior when target is a directory is that the source filename will be replicated in the target directory, with the addition of a .encrypted suffix if encrypting and a .decrypted suffix if decrypting.

Add the ability for the user to specify a custom suffix to use instead.

[mattsb42-aws]

Added in https://github.com/mattsb42-aws/aws-encryption-sdk-cli/commit/41d44bf79f44cbc3d3e6ddf299a9d7d670c93860

[mattsb42-aws]

Providing an empty string fails.

[juneb]

In cmd.exe, the --suffix parameter with no value fails, but specifying an empty string appends an empty string suffix. We should make this work.

Also, if you specify a value in quotation marks, even single quotes, the file name includes the quotation marks. That's not an expected result.

(py) c:\ps-test>aws-crypto --encrypt --master-keys key=%cmkARN% ^
More?                     --encryption-context Dept=IT --suffix '' ^
More?                     --input .\TestDir --recursive --output .\TestEnc

(py) c:\ps-test>dir .\testenc
 Volume in drive C is OSDisk
 Volume Serial Number is DA92-2FB6

 Directory of c:\ps-test\testenc

10/06/2017  03:34 PM    <DIR>          .
10/06/2017  03:34 PM    <DIR>          ..
10/06/2017  03:34 PM             2,723 cool-new-thing.py''
10/06/2017  03:34 PM               630 Employees.csv''
10/06/2017  03:34 PM               595 Hello.txt''
               3 File(s)          3,948 bytes
               2 Dir(s)  163,718,578,176 bytes free

[mattsb42-aws]

#33 created to track the empty suffix feature