stdlib: update stdlib docs with formatting, grammar and spelling fixes

[Hoverth]

Fixes a number of issues so that the generated documentation (in amber-docs/#39) looks better and is more understandable.

Should fix #459.

[Mte90]

There is already a ticket for multiline comments #459

If we fix that a lot of issues in the documentation generated are solved.
Anyway this PR fixes various english issues already reported by @mks-h

[Hoverth]

I'm aware of the ticket, although in my opinion it's better for both to be done at once, as the lines already in the multi-line comment doesn't follow the typical tense for describing functions, so it makes sense to solve both at once.

This should improve things for amber-lang/amber-docs#39 quite a bit.

[Mte90]

Yeah but if you see the date.ab file there are comments that still will be broken on rendering because they aren't in multiline (the part minute seconds etc).
So we need a fix anyway in Amber

[Hoverth]

I'm not terribly sure what you mean, I tested all the files after i finished with them by using amber --doc $path to make sure that the generated markdown files all were formatted correctly

[KrosFire]

Looks good. Good job