Update changelog for 0.3.0

[MDLC01]

This reorganizes the existing changelog entries in a way that is hopefully easier to read quickly.

[MDLC01]

@T0mstone I reordered what you suggested, and more. Tell me what you think.

[MDLC01]

Arguably, pee should be listed under "Miscellaneous technical" and mapsfrom.* under "Arrows". What do you think?

[T0mstone]

Not sure about pee: It doesn't really fit my conception of "technical", but maybe I'm misunderstanding what that means.
Similarly, I'd think it makes more sense for the tacks to be in "Mathematical symbols".
(Also, do we want to capitalize "Symbols" and "Technical"? The latter is capitalized in the 0.2.0 section)

For mapsfrom.*, I think either way has its benefits. They are arrows and literally just aliases for already existing arrow variants, so putting them under "Arrows" would make sense. On the other hand, I think these carry a bit more of an intent of use in formulas/equations, rather than diagrams, so having them under "Mathematical symbols" also makes sense.

[MDLC01]

Not sure about pee: It doesn't really fit my conception of "technical", but maybe I'm misunderstanding what that means.

Let's keep it there then, as it's mostly used for the Weierstrass elliptic function, which is a mathematical concept as far as I can tell.

Similarly, I'd think it makes more sense for the tacks to be in "Mathematical symbols".

I would disagree with this as they are mostly used in formal logic, which I don't think is strictly a mathematical field.

Also, do we want to capitalize "Symbols" and "Technical"?

We should only use title case for actual headings imo.

On the other hand, I think these carry a bit more of an intent of use in formulas/equations, rather than diagrams, so having them under "Mathematical symbols" also makes sense.

I agree with this.

[laurmaedje]

Thanks for keeping the changelog up to date. It really makes things much easier for me!