Improved bold, italic. Added scratched.

Bold and italic as delimiters instead of keywords supporting sentences with spaces.
Scratched text (~~text~~) shown as underlined.

I took the following text from [here](https://github.com/adam-p/markdown-here/wiki/Markdown-Cheatsheet#code-and-syntax-highlighting)
```
Emphasis, aka italics, with *asterisks* or _underscores_.

Strong emphasis, aka bold, with **asterisks** or __underscores__.

Combined emphasis with **asterisks and _underscores_**.

Strikethrough uses two tildes. ~~Scratch this.~~
```
With your _userDefinedLang_ file, sentences with spaces don't look correctly. 

Unfortunately, my solution don't solve combined sentences.

Besides, scratched text shows underlined.