Test and improve Markdown rendering

[nefarius]

• [x] The colors of some elements like hyperlinks need to be adjusted to the used ImGui styles, currently the contrast is off making some elements very hard to see.
• [x] The spacing before and after heading paragraphs is too big, decrease to more sane values.
• [x] Images don't get rendered yet.
• [x] URLs missing the proper syntax are not highlighted and clickable.
• [x] Clickable images navigate to the image URL instead of the underlying link URL
• [x] Emojis do not render properly, assume they need to be supported/provided by the loaded fonts, investigate.

[nefarius]

Working on embedded images support 👀

[nefarius]

Embedded images from remote resources now get downloaded and displayed correctly:

[nefarius]

Hyperlink color contrast fixed:

[nefarius]

Tested setting the flag MD_FLAG_PERMISSIVEURLAUTOLINKS to see if that would support GitHubs auto-generated plain changelog URLs but it doesn't a 100%:

I'll just ignore this; if folks need proper links, use proper Markdown in the summary 😎

[nefarius]

Found the best compromise:

Surround the URL like so:

**Full Changelog**: <https://github.com/nefarius/HidHide/compare/v1.4.192.0...v1.4.202.0>

And it gets rendered properly without any additional flags 🥳

[nefarius]

Debugging the clickable image URLs, when an "IMG" is rendered, it checks for mouse-over and release to trigger the link navigation, in the function imgui_md::SPAN_IMG it first sets the member m_href which parses the fragment http://sharex.nefarius.at/u/donation-button.gif)](https://docs.nefarius.at/Donations/) into:

	Name	Value	Type
▶	m_href	"http://sharex.nefarius.at/u/donation-button.gif"	std::string

So instead of opening the underlying link, the URL to the image displayed is used in the open_url overload.

IDK if this case has not been tested properly or if this is considered expected behaviour; for me it certainly isn't 😛 Let's try to fix this.

[nefarius]

Everything I found is fixed 😄