Refactor all fields such that the user need not call #validate explicitly

[haleyga]

Currently, fields are constructed without throwing errors. The user calls #validate on each object and catches errors at validation time. Consider refactoring such that fields are validated on construction, and errors are thrown immediately rather than waiting for an explicit #validate call.

This would force users to handle construction-time throws, but I believe this is more intuitive than a silent #new followed by an explicit #validate call.

[haleyga]

I'm rethinking this approach. Considering the high-performance environment in which a FIX engine will likely be run (and given JavaScript's inherent performance shortcomings), try/catch blocks may impose an unnecessary overhead.

Perhaps a #validate pattern is preferred in such a situation. An explicit validation that simply returns a boolean should provide much better performance than try/catch blocks and throws (at the expense of the developer).