[Feature Request] Highlight improvements

[PROPHESSOR]

• Dimm highlight colors for dark theme (they're so bright)
  
• Add more colors: blue, cyan, etc.
• Add automatic highlights for some HEX pattern
• Add more highlight methods: text color, background color, underline color, etc

[solemnwarning]

Which of these colour palette(s) do you prefer?

[cgarz]

70 looks the most readable and therefore best imo.
100 does look lovley, but less readable.

[solemnwarning]

I've made all the changes I'm planning on making to highlights for the next release:

• Reduced default intensity of highlight colours when using dark colour schemes
• Allow changing highlight colours, defining custom ones and assigning labels
• Maintain file-specific lists of highlight colours/labels
• Added shortcuts for assigning highlights (Ctrl+1,Ctrl+2,etc by default)

Please do open further issues if you still feel the need for the other changes once you've used the above for a little while.