Allow lowercase variables and reserve future keywords

[Vurv78]

I've been pushing modern E2's syntax to get closer to typescript/javascript so learning E2 is easier and more educational for people wanting to use E2 as a step before moving on to a real world language

The syntax has gotten to a point where it's pretty much identical minus E2 having some extra features. Last things that need to be done are this, #2867 and #2771.
 
Before doing this, need to create a list of keywords to reserve for the future though, here's my proposed keywords

Variables

static super self true false mut var null undefined

Structures

abstract class struct enum union extends implements instanceof new constructor type interface

Macros

macro

Looping

in of

Exceptions

throw throws finally

Modules

mod import namespace export public private pub priv package use

Generators / Async

await async generator gen coroutine (should be done implicitly) yield

Misc

match as typeof

Feel free to comment below any other keywords you think should be reserved. More is better, we can always just remove them later on if it's agreed that we won't implement the actual functionality.

[bjcscat]

client, server, sync, shared

[Vurv78]

using unknown dynamic

[Denneisk]

Can't have constructor without this (Translation: please spare me from writing This instead)

[Vurv78]

Ah yeah always forget JS uses this instead of self.

Should remove self then.

(Ignoring the fact that there's a bunch of non-js keywords here)

[Denneisk]

#3201 will add a warning if any of these are used as an identifier. Hope the impl is alright :P