Added new file full of session variables, plus new types

[Hydrocharged]

I'm sure there are mistakes in here. This was like 85% manually done, and I had lots of mental TODOs while working through it, so I very well may have forgotten to edit a variable, add a note, or change the type. Either way, the majority of variables are here. I did exclude some as I couldn't find any GLOBAL/SESSION or Dynamic information for them, but this is like 98% of the variables.

Now to hook them up and replace our current variable handling.

[zachmu]

This is fine for what it is, but I don't know what you have in mind for the new types, esp. things like encode / decode. Listing the full set of supported system vars is definitely important, so it's good to get that in.

There are a bunch of other outstanding issues with variable assignments, like that we don't differentiate between @@timestamp and @timestamp for example, either in the analysis logic or the session storage. We really need to do that, since it's totally fine for a single var to have 3 different values: a global system value, a session system value, and a local var value.

Anyway, LGTM, looking forward to the next part