update TwoDTurb docs

[dkarrasch]

use unicode symbols

[codecov]

Codecov Report

Merging #36 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #36   +/-   ##
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  Coverage   98.64%   98.64%           
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  Files           6        6           
  Lines         518      518           
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  Hits          511      511           
  Misses          7        7

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[navidcy]

thanks @dkarrasch
actually, the docs are bit outdated and we should re-think our strategy a bit on keeping them up to date.

[dkarrasch]

One strategy could be to use https://github.com/JuliaDocs/DocStringExtensions.jl. Basically, you pepper your code with comments that would be helpful for code development anyway, and then build most of the documentation by macros. I.e., have docstrings build from the struct definitions, signatures of functions, fields of structs, etc. In the markdown file, one could have a few unspecific lines like "The package provides the following types/functions" and let Documenter fill in the details. Then you don't need to worry about the "hard-coded" text in the markdown, and only keep the docstrings up-to-date in the code.