Add custom elementary syntax styles

[micahilbery]

This adds custom styles for syntax highlighting based on the elementary color palette.

fixes #29

[hanaral]

@micahilbery is this supposed to fix the long-standing issue of the highlight cursor colour in the solarised theme being the same?

[micahilbery]

@hanaral If you're talking about the bracket highlighting and selection highlighting being the same then yes this fixes that.

[jeremypw]

If you're talking about the bracket highlighting and selection highlighting being the same then yes this fixes that.

It looks like that the selection style is applied in preference to the bracket-match style so brackets that are both matching and selected only get the selection style. Presumably this behaviour is controlled by gtksourceview-4.

[jeremypw]

@micahilbery Will you be addressing the issue with gutter colors?

[micahilbery]

Yes, I hope to work on it today. Sorry for the delay. My day job and seasonal plans have pretty well wiped out my free time.

[micahilbery]

I've updated the style so that we match classic and tested the git gutters. Afaict everything seems to be working as it should. Sorry this took me so long to get to.

[jeremypw]

Thanks - I'll try these out for a while to see if any issues arise.

[jeremypw]

I've merged this PR into my 'merge-dev-fixes- branch for dog-fooding.

Do far I've noticed that it is harder to see the selected text, especially for solarized-light:

However, it is easier to distinguish selected brackets from highlighted brackets.

Is there a reason why selected text in the dark version is inverted in color whereas in the light version it isn't?

[jeremypw]

I can confirm that the gutter colors are now working.

[jeremypw]

@micahilbery I'm inclined to merge this as @danirabbit is :+1: Just one question: "Follow System Style" uses the standard "solarized-light" and "solarized-dark" styles - is that intended?