Implement Capitalization

[lepasq]

Fixes #100 (adds lower and upper case styling).

I used an example, in which h1 and h3 tags were wrongly capitalized. This produced the following output:

You can rerun the example, by running go run examples/capitalization/main.go and by making h1 upper case and h3 lower case by adding the following lines to styles.go:

[lepasq]

I realized that upper should make all letters upper case, not just the initial one.
This is what the output looks like now, using the same input text as before:

[muesli]

This looks nice, thank you! I imagine an option for using title case would also be appreciated. Could you also try and add a test-case for these styling options?

[lepasq]

Sure, I'm going to work on that!

[lepasq]

I got rid of the example file, since there now is a unit test for the capitalization options.
I wasn't sure if there is a way to assign a value to a nil-pointer without creating a new variable.
Therefore, I used the following workaround:

var s bool = true
var p *bool = &s

style := DarkStyleConfig
style.H1.Upper = p
style.H2.Title = p
style.H3.Lower = p

Is there a cleaner way to do this?

[muesli]

Is there a cleaner way to do this?

Only slightly, but still nicer to read:

b := true
style.H1.Upper = &b

[lepasq]

Thanks! I updated that section in the code.

[muesli]

Thank you for your contribution! ❤️

[lepasq]

You're welcome!