ExecType Fill is replaced with Trade in FIX 4.3

[cotsuka]

When testing FIX 4.4+ connections with an AppDataDictionary, the Execution Report ExecType tag value results in a message reject: Value is incorrect (out of range) for this tag. Looking at Appendix 6-F. Replaced Features and Supported Approach and confirming with the tag values in the XML files from quickfixgo's spec folder, ExecType_FILL is no longer a valid enum value.

Sorry for sending a PR out of the blue. Let me know if you'd like me to make any changes.