Write output from the ASN1_Codec::filetest function directly to stdout

[iyourshaw]

Adds one line to filetest() to write to stdout.

See the issue for rationale:
Support using asn1_codec as a decoder in command-line mode

Tested by:

• Building and running asn1_codec in Docker and verifying that the unit tests at /build/acm_tests pass.
• Running the demo app here that uses asn1_codec in command-line mode, and verifying that it can produce decoded output from asn1 hex inputs: https://github.com/iyourshaw/asn1-codec-java

[payneBrandon]

lgtm!

[dmccoystephenson]

Looks good!