add basic latex display support if unicodeit is installed

[HDembinski]

If the external package unicodeit is installed, translate variable names which contain simple LaTeX into unicode that mimics the correct LaTeX rendering. This only works for very basic LaTeX like $\alpha$.

[HDembinski]

unicodeit could in principle render more complex LaTeX code, if it used a better LaTeX parser. The current code just does simple search and replace, and cannot handle code such as $D^{\ast\ast}$ correctly, since it does not understand the grouping with curly braces.

[zjkjsd]

Indeed! This is awesome! Thank you for adding this feature~