Add full URL support for the `--source_file` and `--schema_file` options

The `--source_file` and `--schema_file` options currently imply `file://` if using fully qualified URL syntax. Other protocols, such as `http://`, `ftp://` and `ws://` should be possible to resolve in this way, although `ws://` would only be applicable as a protocol under `--source_file` and not `--schema_file` and would need to be implemented in a manner similar to the recent stdin support addition.

Example:

```
txcode --schema_file https://raw.githubusercontent.com/SunGard-Labs/fix2json/master/dict/FIX50SP2.CME.xml --source_file ftp://ftp.cmegroup.com/SBEFix/Production/TradingSessionList.dat --factory fix --source_file_format_type line_delimited
```