Change cheatsheet color scheme to a light one

So that it's more printer-friendly.

Resolves issue: #1162

Other changes:

- README: Cheatsheet: Document how to generate PNGs
- README: Improve "LaTeX" typography
- prelude-cheatsheet.pdf: Repl. file copy w/ symlink

README.md

@@ -494,13 +494,22 @@ Use `C-h k <key>` (`<key>` are the ones listed on the left) or `C-h f <function>
 
 #### PDF generation
 
-Install [latex](https://www.latex-project.org/get/)
+Install [LaTeX](https://www.latex-project.org/get/)
 
 ``` bash
 cd modules/doc
 pdflatex prelude-cheatsheet.tex
 ```
 
+#### PNG generation
+
+Install [Poppler](https://poppler.freedesktop.org/)
+
+``` bash
+cd modules/doc
+pdftocairo -png -singlefile prelude-cheatsheet.pdf cheatsheet
+```
+
 ## Automatic package installation
 
 The default Prelude installation comes with a bare minimum of

modules/doc/prelude-cheatsheet.tex

@@ -12,15 +12,16 @@
 \usepackage{calc}
 \usepackage{tcolorbox}
 
-\pagecolor{black}
+\definecolor{default}{HTML}{333333}
+\definecolor{heading}{HTML}{000000}
+\definecolor{command}{HTML}{666666}
+\definecolor{key}{HTML}{268BD2}
 
-\definecolor{heading}{HTML}{5DCACB}
-\definecolor{command}{HTML}{D8DA78}
 \renewcommand\section[1]{\bigskip\par\textbf{\color{heading}\large#1}\smallskip}
 \renewcommand\subsection[1]{\smallskip\par\textbf{\color{heading}#1}}
-\newcommand\humanreadable[1]{{\par\color{orange}\small\sffamily#1}}
+\newcommand\humanreadable[1]{{\par\color{default}\small\sffamily#1}}
 \newcommand\meta[1]{\textlangle\textit{#1}\textrangle}
-\newcommand\keyify[1]{\color{pink}\ttfamily#1}
+\newcommand\keyify[1]{\color{key}\ttfamily#1}
 \newlist{keylist}{description}{1}
 \setlist[keylist]{
   topsep      = 1pt,

prelude-cheatsheet.pdf

@@ -0,0 +1 @@
+modules/doc/prelude-cheatsheet.pdf