Simplify/remove ixml.js

[kadler]

ixml.js includes various definitions for XMLSERVICE tags and attributes. This is way overly complicated and over-engineered.

For instance, I_XML_ATTR_KEY_ERROR is defined to the string "error". Having definitions like this can be useful, however:

• this string will never change as it would break compatibility
• "error" is in the key name, so you already have to know what you're looking for
• I_XML_ATTR_KEY_ERROR is longer and more complicated to type (caps, underscores)

This abstraction brings no benefits whatsoever, while imposing extra mental effort to understand and parse the abstraction.

A better model would be to use Javascript template literals or possibly a template engine (though this might be overkill as well).

[markirish]

I think when we start removing these constants, and using the literals strings in the templates for the nodes, we will see that there are only a few dozen 'node templates' with a few options for each that need to be accounted for. Also the fact they they are all declared, and then all exported makes the file a lot larger than it will eventually end up.

I think native template literals are a great idea, and should probably be the starting point until we find a deficiency.

[abmusse]

@kadler

After merging PR #80 can we close this issue?