updated some themes so they can support lightweight markups such as txt2...

...tags

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Here are some coloschemes modifications so they can support markups.

I've made, when possible, by default headings = red so we can see them well, strong = blue (no need to be red, it's already bolded so we see it well), emph = brown (almost red), underligne when it exists is green. Code, blockquote too is green. Links are blue.

I've added comment_markup not to interfere with the other comment mark. By default this one is blue, and since there are already a few colors, I found it was better to have comments in grey. Since default fonts are black, it make comments less visible and interfering.

preproc and postproc are specific to txt2tags but since it's important for us to know if it's a preproc or a postproc, I wanted to have them different from the "preprocessor" color.

If it pleases you, I'll add some new colorschemes such as solarized and steampunk.