Add missing FVector2/3/4 methods to Vector classes

**Issue by [error454](https://github.com/error454)**
_Wednesday Jul 03, 2019 at 02:40 GMT_
_Originally opened as https://github.com/SkookumScript/SkookumScript-Plugin/issues/4_

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**Is your feature request related to a problem? Please describe.**
When you do a lot of vector work in C++, you get used to using certain helpers and methods on the vector types. Functions like `GetUnitAxis` for example, which aren't even exposed to BP but are invaluable.

**Describe the solution you'd like**
It would be great to have feature parity between the C++ `FVector` types and the sk `Vector` types.

**Additional context**
This may be brute-force manual additions to the `Vector2/3/4` classes, see [Vector2 impl](https://github.com/SkookumScript/SkookumScript-Plugin/blob/005abdae66d1a591092414a6f7d1a2880f387bb9/Source/SkookumScriptRuntime/Public/Bindings/VectorMath/SkVector2.hpp). But it sure would be nice if we could scrape and auto-generate bindings with some meta-programming and then set it loose on the entire FMath library. Unfortunately, many of the math methods do not have `UFUNCTION` macros so using UHT isn't an option.